Working with Serena Williams' former coach Patrick Mouratoglou, Halep enjoyed a promising 2022 following an injury-hit 2021 campaign, reaching the semi-finals at Wimbledon and moving up to ninth in the WTA rankings.
However, the two-time major champion has struggled since winning the Canadian Open last month, losing in the first round at the US Open.
Prior to her success in Canada, Halep was forced to retire in the second round of the Citi Open after enduring breathing difficulties, and the ongoing problem prompted surgery this week, with Halep disclosing she also elected for cosmetic changes to the nose.
The former world number one will miss the final events on the WTA Tour this year, but she explained the procedure was necessary.
She wrote on Twitter: "As you all know already because I've talked about it many times, in February, I was very close to stopping tennis because I didn't believe I have enough power to come back to top 10. I was going through many anxious moments and I thought it is time to stop cause it is emotionally unhealthy.
"Then I was lucky to discover Patrick's academy where I felt so much passion that it gave me back my passion for tennis. Thanks to Patrick, I slowly started to believe that I still can play a good level of tennis.
"My goal was very clear: I gave myself one year to get back to top 10. And faster than I ever expected, in only two months, I was back to top 10. Goal achieved!
"But then, when I lost at the US Open, I realised that I'm completely exhausted mentally. Having problems with the breathing for many years already and becoming worse with the time, I decided to follow the advice of my doctors and do the needed surgery.
"I could never do it earlier because I never found the necessary three months for the recovery, because tennis was always the first priority in my life. But I felt it's the right time to do it and also to do something for myself as a person.
"That is why I did also the aesthetic part, that I wanted to do for a long time as I did not like my nose at all. So I did it, I solved the functional part and the aesthetic part.
"I don't know how long the recovery will take, for the moment I am not thinking about anything but recovery. What is sure, is that this year I won't be able to compete in any official tournament anymore.
"My 2022 season is over. 2022, you have been an interesting year full of everything! See you on court, 2023! I feel I still have a lot to do on a tennis court and still have some goals."
World number three and two-time grand slam winner Halep last month withdrew from the French Open after sustaining a calf injury.
The Romanian is targeting a return in time for the grass-court swing and will feature at the new WTA 250 event in Germany.
Designed with preparation for Wimbledon in mind, the Bad Homburg Open will run from June 20-26.
Halep, who has accepted a wildcard, is one of three former Wimbledon winners to be participating, alongside Angelique Kerber and Petra Kvitova.
"I have some good news to share with you," Halep said in a video posted to her official Twitter account.
"I am super excited to announce that I will be playing for the first edition in Bad Homburg and I am looking forward to seeing all of the fans in the stands."
Halep, who has also triumphed at Roland Garros, overcame Serena Williams 6-2 6-2 in the 2019 Wimbledon final.
The grand slam in London did not take place last year due to the coronavirus pandemic.
The former world number one, competing at the Moscow event for the first time since 2013, won 6-1 6-4 to set up a meeting with Veronika Kudermetova, who survived a marathon contest with qualifier Oksana Selekhmeteva.
Anett Kontaveit, who won the title in Ostrava last month, prevailed 6-3 6-3 against Katerina Siniakova. Another seed, Wimbledon quarter-finalist Ons Jabeur, retired against Ekaterina Alexandrova when trailing 6-1 1-0.
Andrea Petkovic also progressed when Jelena Ostapenko had to halt proceedings in their third set, while seventh seed Elena Rybakina lost in straight sets to Olympic silver medallist Marketa Vondrousova.
At the Tenerife Open, Camila Giorgi progressed past Aliona Bolsova 7-6 (7-4) 3-6 6-4 despite giving up two penalty games due to repeated indiscretions when line calls were called into question.
Fifth seed Viktorija Golubic lost in straight sets to Arantxa Rus, while Alison Riske was dispatched 6-1 6-4 by Donna Vekic.
Seventh seed Clara Tauson defeated Heather Watson via a final-set tie-break, while Varvara Gracheva won in the same vein against third seed Sara Sorribes Tormo in a match lasting nearly three and a half hours.
Top seed Elina Svitolina was one set up against Maria Camila Osorio Serrano when their match was suspended for the night.
Halep's last grass-court match was the impressive 6-2 6-2 defeat of Serena Williams in the 2019 Wimbledon final.
While Monday's triumph may not have been of comparable importance, the 6-1 6-4 win was a positive step in Halep's preparation for a return to SW19 later this month.
After saving three break points in the very first game, the former world number one rarely looked in trouble against her Ukrainian opponent, breaking Tsurenko's serve at the first opportunity.
She repeated the feat to go 5-1 up before serving to love to close out the set, though Tsurenko showed a bit more fight at the start of the second – only one of the first five service games was a hold.
Halep ultimately weathered the storm, however, taking her chance to go 5-4 up and once again served to love to wrap up the match.
Seeded second, Halep was the only seed in action on Monday and will meet home favourite Harriet Dart next, with the Brit impressively seeing off Camila Osorio – ranked 45 places better off – 6-2 6-0.
In Berlin, fourth and sixth seeds Karolina Pliskova and Daria Kasatkina secured their passage to the last 16.
Pliskova struggled initially against Kaia Kanepi but went on to produce two near-flawless sets to progress 6-7 (6-8) 6-0 6-0 – Kasatkina also came from behind, with an ankle injury to Anhelina Kalinina potentially aiding her 5-7 6-3 6-1 victory.
Bianca Andreescu was also among the winners in Berlin, with the Canadian beating Katerina Siniakova to claim only her second career success on grass.
The two-time grand slam champion has been sidelined since suffering a calf injury during her a second-round match against Angelique Kerber at the Internazionali d'Italia in Rome last month.
Halep was due to feature in a new grass-court tournament in Bad Homburg, which starts on Sunday, but is not ready to return.
The world number three is determined to be back at full fitness to feature in the third major of the year at the All England Club.
She revealed in a social media post on Saturday: "I will not compete because my calf is not ready for a competition. I feel sorry about that and sad, because it's a beautiful place.
"I will keep practising because I really want to be able to play at Wimbledon, but for now I have to take care of my body and see how the recovery is going.
Wimbledon gets under way on June 28, having been cancelled last year due to the coronavirus pandemic.
Former world number one Halep was due to face Australia's Daria Saville in the round of 64 on Thursday but felt unable to contest the match.
Halep said she sustained a thigh injury during her Indian Wells semi-final defeat to Iga Swiatek the previous week and it caused her discomfort again while training on Wednesday.
The 30-year-old two-time major winner expects to sit out the Charleston Open and will miss the start of the Billie Jean King Cup.
In a tweet posted on her official Twitter account, Halep wrote: "While I was practising in Miami yesterday I felt a sharp pain in my left leg.
"I had been struggling with the thigh since my semi-final in Indian Wells and hoped it would improve, but I went for an MRI last night and unfortunately it showed a tear.
"My body needs time to heal and as a result I will be out of competition for three weeks. This means I have had to make the super tough decision to pull out of Miami, Charleston and Fed Cup [Billie Jean King Cup].
"While it feels like really disappointing news to share, I am keeping the confidence from my great start to the year and am motivated to do everything to be ready for the clay-court season.
"Thanks for your continued support through the highs and lows."
Lucky loser Harmony Tan will take Halep's place in the draw.
Wimbledon was this week cancelled due to the coronavirus pandemic, which has spread to over a million people worldwide.
It will mark the first time since World War Two that the grass-court grand slam has not been held.
Halep clinched her second major title at the All England Club last year, crushing Serena Williams in straight sets in the final.
In an interview with The Times, she said of not being able to defend her title this year: "Even though the cancellation of Wimbledon felt inevitable after the past few weeks, I had hoped it might somehow find a way to stay on the calendar as it is such a special tournament.
"So Wednesday was a sad day and I thought back to some of the happiest emotions of my life last year at the All England Club.
"I will miss going back to see Centre Court, the scene of that amazing final last year. I will miss seeing my name on the wall and all the nice things you get as a member of the club. I will miss the grass, a surface I finally fell in love with.
"I will miss wearing white. And I will miss the feeling of belonging as part of the huge tradition that Wimbledon represents.
"I know that Wimbledon looked at other opportunities to stage the championships. They looked at playing without spectators and postponing, but none of these options worked because of the nature of the surface and the high number of people involved. It makes sense to call it off now so that we are all mentally prepared for it, rather than to wait and let people down at the last minute.
"The club sent me a nice email on Wednesday. I had previously been discussing with them the prospect of doing some filming as the defending champion in the lead-up to the tournament. Hopefully we can do those things next year instead.
"In a positive way, I will have the rare and special honour of being a reigning Wimbledon champion for two years. I love the tradition in which the defending champion gets to open play on Centre Court, so I hope I can still do that next year as that will be something to savour."
The ATP and WTA Tours are both suspended and Wimbledon's cancellation has led to talk of the rest of the 2020 season being wiped out.
"The virus is like nothing we have ever faced before, and it's important to remember that tennis is not important in comparison to this life-threatening opponent," added Halep.
"At this point, I do not want to speculate on whether the remainder of the 2020 season will be shut down. We have to see clear signs that the virus is under control.
"We have to let our governments and medical staff do their jobs, and when life starts returning to normal, then we can start to think about tennis."
Halep defeated 10th seed Gauff, who had beaten Naomi Osaka, Elena Rybakina and Aryna Sabalenka this week, in one hour and 47 minutes.
The Romanian 15th seed was broken five times and sent down eight double faults, but found the edge with speed, finesse and power.
The win means Halep has won the third most matches (36-10) on the WTA Tour this season, behind only top-ranked Iga Swiatek (49) and Wimbledon finalist Ons Jabeir (37).
Halep's improved form comes after she teamed up with Serena Williams' ex-coach Patrick Mouratoglou in April following a difficult 2021 season.
"Before I met him I was super down with my motivation," Halep told reporters. "I couldn't really work, keep working. I was almost done with tennis. He brought this fire back and the motivation. He trusted that I still can play good tennis and he transferred this to me."
The 2018 French Open and 2019 Wimbledon champion added: "Physically I'm good. Mentally I'm good, so I think it's all positive."
Halep, who won the Canadian Open in 2018, has reached the semi-finals for the fifth time in her career where she will take on seventh seed Jessica Pegula.
Pegula got past Yulia Putintseva 6-3 6-3 in one hour and 21 minutes. Qualifying for the last four at the Canadian Open for the second straight year.
Brazilian Beatriz Haddad Maia maintained her Canadian Open run, having ousted Swiatek in the third round and local favourite Leylah Fernandez in the second, with a 2-6 6-3 6-3 victory over Tokyo Olympics gold medalist Belinda Bencic in two hours and 11 minutes.
Haddad Maia became the first Brazilian to reach the semi-finals of a WTA 1000 tournament. She will face Karolina Pliskova in the semi-finals after the Czech 14th seed beat Qinwen Zheng 4-6 6-4 6-4.
World number three Halep had claimed straight-set wins over Ekaterina Alexandrova and Marketa Vondrousova en route to the semi-finals, but met her match in the form of Belarusian Sabalenka, who triumphed 6-3 6-2.
A nine-time singles champion, Sabalenka made it into a 14th career final without conceding a single break, as she managed to keep Romanian Halep at arm's length.
Standing between Sabalenka and a 10th singles title is world number one Barty who, on her 25th birthday, came from behind to defeat Elina Svitolina 4-6 7-6 (7-5) 6-2.
Making her tournament debut in Stuttgart, Barty had overcome Laura Siegemund and Karolina Pliskova, but found herself at 5-4 down in the second set, with Svitolina serving for the match.
The fourth seed failed to take her chance, with Barty breaking and subsequently biting back in the tie-break, before carrying the momentum into the decider to claim a third straight win over Svitolina.
Top seed Elise Mertens made it to her second Istanbul Open as she saw off her doubles partner and birthday girl Veronika Kudermetova 6-1 6-4.
It means Mertens will be playing in two finals on Sunday, as she pairs up with Kudermetova again in the doubles showdown against Nao Hibino and Makoto Ninomiya.
Mertens' win ended Charleston champion Kudermetova's nine-match winning streak, and set up a final against the unseeded Sorana Cirstea, who defeated Marta Kostyuk 6-4 6-4.
Cahill said Halep's "integrity is faultless" and insisted there was "no chance" she would have deliberately or wittingly taken a banned substance.
It was made public on Friday that 31-year-old Halep tested positive for roxadustat while competing at the US Open in August.
Halep, who has been provisionally suspended, said she felt "confused and betrayed" by the news. She has not explained why, or by whom, she senses a betrayal.
She now risks a ban from tennis and faces a battle to clear her name, which she has said she is determined to achieve.
Cahill was Halep's coach when she landed her first grand slam title at Roland Garros in 2018, and he pointed to his experience of an athlete who was meticulous about checking anything she ingested.
He wrote in a statement posted on Instagram: "Firstly, and most importantly, there is NO chance Simona knowingly or purposely took any substance on the banned list. None. Zero.
"She is an athlete that stressed about anything prescribed to her by a medical professional [which was rarely], or about any supplement that she used or considered. Simona wore out the words 'please double check this, triple check this to make sure it’s legal, safe and permitted. If you are not sure, I'm not taking it.'"
Australian Cahill has also worked with players including Lleyton Hewitt, Ana Ivanovic, Andy Murray and Andre Agassi. He rates Halep as a player and person of the highest order.
When they stopped working together in September 2021, Halep thanked Cahill "for making me a better tennis player and a better person".
Cahill wrote on Sunday: "Simona's integrity is faultless, she respects her peers, she loves the game and she always has her feet firmly planted on the ground as a humble, approachable champion.
"Honesty has always been her greatest strength and her biggest weakness. We would often laugh about the fact that she can't act and can't tell a little white lie.
"She wears her mood on her shoulder for the world to see, for good and for bad. That is Simo. What you see is what you get. She built an amazing career and legacy by doing things the hard way. The right way.
"Due process will now follow to reveal answers to many questions. As Simona said, the hardest match of her life starts now. I believe in her. I always have and can honestly say never more than right now on this particular issue. I stand with Simo."
Halep beat Caroline Garcia in the second round in Florida on Thursday, but an issue with the world number three's right shoulder prevented her from facing Anastasija Sevastova.
The two-time grand slam champion said: "I'm very sorry to I have to pull out of the singles and doubles at the Miami Open, but my injury doesn't let me play here as expected.
"I'm sad that I can't continue, I wanted to come here to give my best and play many matches but unfortunately I can't.
"Hopefully next year I will come back healthy and better."
Sevastova will face either French Open champion Iga Swiatek or Ana Konjuh in the round of 16.
Osaka, who won the most recent of her four grand slam titles last year at Melbourne Park, has looked in fine form this week in her first appearances since returning from the break she took from tennis last year.
The top seed beat Alize Cornet, Maryna Zanevska and Andrea Petkovic en route to the semi-finals, but could not compete against Veronika Kudermetova on Saturday, citing an abdominal injury.
Osaka explained that her body had taken a hit from playing such intense matches in consecutive days, and she instead is looking to rest and recover ahead of the first grand slam of the season, which starts on January 17.
"Sad to withdraw due to injury from my match today, my body got a shock from playing back to back intense matches after the break I took," Osaka tweeted.
"Thank you for all the love this past week [Red heart] I’ll try to rest up and I’ll see you soon!"
Osaka's injury has prevented what looked to be an enticing showdown with Simona Halep, who guaranteed a place in a WTA Tour singles final for a 13th successive season by beating Chinese teenager Zheng Qinwen 6-3 6-2.
Halep's first final came in 2010 and she has taken just a week to get back into her stride after an injury-ravaged 2021 season.
The Romanian, a two-time grand slam champion, went into the week ranked at world number 20, her lowest position at the start of a season since 2013.
However, she has now reached at least the semi-final stage in three successive tournaments, and she will fancy her chances against third seed Kudermetova, who is into her third singles final.
Muguruza, who won the WTA Finals title at the end of last season, was cruising at 6-0 3-0, but 31-year-old American Riske, despite tossing her racket in frustration, refused to give up. Incredibly, she won 12 of the next 13 games to reach the third round at the expense of the world number nine.
"After the first set, it literally could not get any worse," Riske said in her on-court interview following a 0-6 6-3 6-1 success.
"So if I could try to get two balls in the court we might get somewhere. I was just trying to hang in there. I've played Garbine many times before and it's always been a battle."
This was Riske's fifth match against Spanish star Muguruza, and despite losing the first two of those, she had since beaten the two-time grand slam winner twice, albeit most recently at the 2019 US Open.
"I felt if I could get in there a little bit, I was going to have my chances," Riske said. "I know I've beaten her before, and if I could just bring out some of my game, good things were going to happen."
It was world number 53 Riske's 10th career victory against a player ranked in the top 10.
British player Harriet Dart pulled off a shock win over Ukrainian Elina Svitolina, as the world number 122 snatched a 2-6 6-3 6-3 victory over the 12th seed.
Three of the biggest names in the draw took the long route through to the last-32 stage, with Emma Raducanu, Simona Halep and Iga Swiatek taken to a deciding set in their opening matches, having benefited from first-round byes
Raducanu fended off Caroline Garcia 6-1 3-6 6-1, while Halep was a 6-2 4-6 6-2 winner against Ekaterina Alexandrova, the Russian who is playing under a neutral flag.
Polish third seed Swiatek put a slow start behind her to beat Ukrainian Anhelina Kalinina 5-7 6-0 6-1 and is looking to build on her recent Qatar Open triumph. She said: "I'm pretty happy I could turn my head on to fight mode and stay focused, because that was the key I guess."
Last year's Wimbledon runner-up Karolina Pliskova bowed out, the Czech seventh seed losing 2-6 7-5 6-4 to Danka Kovinic of Montenegro.
Gauff would have secured a career-high ranking on the WTA list if she had won Saturday's semi-final, but top seed Jabeur took it 7-6 (7-4) 6-2 to earn a shot at Belinda Bencic in the title match.
Only world number one Iga Swiatek has won more matches on the WTA Tour than fourth-ranked Jabeur this year, who collected a 29th win as she overcame a 3-1 career head-to-head deficit against Gauff to earn the victory.
Gauff, at 18 years and 98 days, would have become the youngest American to reach a grass-court singles final on tour since Andrea Jaeger was runner-up to Martina Navratilova at Wimbledon in 1983.
It was not to be her day though, Jabeur breaking serve for the fourth time in the match to seal victory, encouraged by a large and vocal Tunisian following.
Reflecting on the match, Jabeur said: "When you play Coco you have to have all the shots. She's a talented player; she's very tough to beat. You can see I've lost already three times against her.
"Sometimes she takes it, sometimes I take it, and it was a great match for both of us."
This is just the second WTA tournament where 27-year-old Jabeur has been a top seed.
"I've tried to act like a number one seed on and off the court, and it's a good pressure," she added. "I'm trying to handle it very well and with the support of our Tunisian people here it's great."
Olympic gold medallist Bencic had earlier claimed an impressive 6-7 (6-8) 6-4 6-4 win over Greek second seed Maria Sakkari in the first semi-final.
Jabeur was bettered by Bencic in a hard-fought Charleston final in April, but is determined to secure a different outcome this time.
"I'm definitely going for the final revenge because we played each other at Charleston, and it was a very, very tough match," Jabeur said. "I hope she's tired from today's match."
Rain meant there was no play at the Birmingham Classic on Saturday, with the semi-finals set back to Sunday.
Beatriz Haddad Maia will face 2019 Wimbledon champion Simona Halep, while Zhang Shuai tackles Sorana Cirstea.
Gauff joins other big names in exiting the WTA 1000 event, with Naomi Osaka, Garbine Muguruza, Danielle Collins, Paula Badosa and Maria Sakkari among those crashing out in the second round.
The number 14 seed did not put up much resistance against her Romanian opponent, with Halep winning 6-4 6-4 in just 77 minutes.
Gauff struggled on her own serve in particular, making six double faults and only winning 61.5 per cent of her first-serve points, compared to 83.8 from Halep on hers.
The former world number one and two-time Madrid champion will now face the only remaining top-eight seed in the tournament in the quarter-final, Jabeur, who defeated Bencic 6-2 3-6 6-2.
The Tunisian was out for revenge after losing to Bencic at the same stage last year, as well as in the Charleston Open final last month, and took it well as she sealed victory in just over two hours.
"I came here to take my revenge," Jabeur said after the win. "I wish I played like that in the final in Charleston, to be honest.
"Part of me is very proud of myself for coming today and getting the win. Belinda is such an amazing player and it's very tough to play against her. I'm very happy with the level I showed today, and hopefully this level will continue for the rest of the tournament."
Elsewhere, Victoria Azarenka is out after the number 15 seed was beaten 6-1 6-4 by Amanda Anisimova, who will now face Ekaterina Alexandrova in the last eight after she overcame Marie Bouzkova 6-7 (4-7) 6-0 7-5.
Former world number one Halep was the only player to have won the competition to have reached the last eight, but she was no match for the Tunisian, who won 6-3 6-2 in just over an hour.
After a difficult start to the year, Jabeur has hit her stride in recent times and will be contesting a second semi-final in three tournaments.
While Jabeur caught the eye, particularly with her penchant for a dropshot, Halep proved to be her own worst enemy, recording 12 more unforced errors (20) than winners (eight).
Up next for Jabeur is qualifier Ekaterina Alexandrova, who beat 2019 French Open semi-finalist Amanda Anisimova 6-4 6-3 to reach her first WTA 1000 last-four clash.
Alexandrova has won six of her previous seven meetings with Jabeur.
Meanwhile, Anhelina Kalinina saw her impressive run ended by Jil Teichmann. The Ukrainian had seen off three major winners on the bounce in Sloane Stephens, Garbine Muguruza and Emma Raducanu, but she was beaten in straight sets this time.
Teichmann – who won 6-3 6-4 – will face Jessica Pegula for a place in the final, with the American eliminating Spain's final hope of a home winner in Sara Sorribes Tormo, 6-4 6-2.
Kerber, who won the Australian Open in 2016, had lost the first set to Dayana Yastremska 6-3 and was a break down in the second when she required on-court medical assistance.
After being put through a series of stretches, the former world number one decided she was unable to carry on and retired, allowing Yastremska to reach the last eight of the competition, where she will meet Donna Vekic after her 2-6 7-5 6-1 win over Maria Sakkari.
The most impressive win of the day belonged to Marketa Vondrousova, however, as last year's French Open runner-up claimed a stunning 6-0 6-0 victory over home hope Arina Rodionova, setting up a meeting with another Aussie in the quarters – world number one Ash Barty.
Vondrousova, 20, is taking part in her first tournament since Wimbledon after undergoing wrist surgery in September and will be out for revenge against Barty, who beat her at Roland Garros in June.
Fourth seed Belinda Bencic came through a tight tussle with Julia Goerges to emerge a 7-6 (8-6) 7-6 (7-4) victor, with her last-eight opponent Danielle Collins having significantly less difficulty against fellow American Sofia Kenin – the unseeded 26-year-old winning 6-3 6-1.
The fourth quarter-final will see Aryna Sabalenka go head-to-head with Simona Halep, after the Belarussian sixth seed eliminated Bernarda Pera 7-6 (7-4) 6-2.
Elise Mertens remains on course for a third Hobart International title after the top seed dropped single game in her 6-1 6-0 defeat of Viktoria Kuzmova, setting up a quarter-final with Great Britain's Heather Watson, a 7-6 (7-5) 6-3 winner against Fiona Ferro.
Aussie wildcard Lizette Cabrera claimed a 4-6 6-4 6-4 upset over Kristyna Pliskova, while second seed Garbine Muguruza edged past Ons Jabeur 3-6 6-3 7-6 (7-4) and will face Veronika Kudermetova.
Shuai Zhang, Lauren Davis and Elena Rybakina are also into the quarter-finals following respective triumphs over Kateryna Kozlova, Magda Linette and Alize Cornet on Wednesday.
World number 26 Camila Giorgi battled from a break down in both sets to beat fifth seed Muguruza 7-5 6-3 in an hour and 53 minutes.
That meant 12th seed Giorgi made her second straight quarter-final, following a last-eight appearance in Birmingham, and will next face Viktoriya Tomova, who defeated Kirsten Flipkens 3-6 6-3 6-4.
Jil Teichmann, the 10th seed at the tournament, was a notable second-round elimination, falling to a 7-6 (9-7) 4-6 6-3 defeat to Briton Harriet Dart, who later triumphed 6-4 2-6 6-4 over Marta Kostyuk.
Dart's fellow Briton Katie Boulter stunned last year's Wimbledon runner-up Karolina Pliskova in the second round but had no such luck against Petra Kvitova, losing 5-7 6-0 7-5.
Beatriz Haddad Maia, the winner at the Birmingham Open last week, extended to a 12-match winning streak with a 6-1 6-2 victory over Jodie Burrage.
Jelena Ostapenko also progressed after Madison Keys retired when 6-3 down and will next face Anhelina Kalinina, who battled to a 6-3 2-6 6-3 win over 16th seed Yulia Putintseva.
While seeds fell at Eastbourne, there were not as many shocks at the Bad Homburg Open, where Angelique Kerber defeated Lucia Bronzetti 6-2 6-3 to reach the quarter-finals.
Fourth seed Simona Halep also made the last eight with 6-0 6-3 victory over Tamara Zidansek and will meet Amanda Anisimova after she won an All-American match against Ann Li 6-0 6-2.
Alize Cornet downed Tatjana Maria 7-6 (7-4) 6-4 to tee up a clash with Kerber, while Bianca Andreescu will meet top seed Daria Kasatkina after defeating Katie Swan 6-4 6-4.
Former world number one Muguruza withdrew from her quarter-final against Veronika Kudermetova on Thursday.
The two-time grand slam winner is scheduled to face a qualifier in the first round of the Australian Open on Tuesday. She is in the same quarter of the draw as Karolina Pliskova, Elina Svitolina and Angelique Kerber.
Muguruza tweeted: "I'm sorry I could not play today. I've had a fever for several days and this morning my body said 'enough'.
"I'll rest today and hope to travel to Melbourne tomorrow. I hope to be able to play [the Australian Open].
"I want to thank all the fans in Hobart for their support and love. I hope to return soon."
Heather Watson beat top seed Elise Mertens 6-7 (5-7) 6-4 7-5 to reach the semi-finals, while Kudermetova will take on Zhang Shuai.
At the Adelaide international Simona Halep suffered a 6-3 6-2 quarter-final loss to Aryna Sabalenka.
Second seed Halep lasted just one hour and nine minutes against Sabalenka, who reeled off seven straight games to take the first set and move 5-0 up in the second.
The Wimbledon champion won the next two games but was unable to hold serve to stay in the match.
Sabalenka will take on Dayana Yastremska, who beat Donna Vekic 6-4 6-3, in the semi-finals.
Top seed Ash Barty repeated her French Open final victory over Marketa Vondrousova to reach the final four in Adelaide.
Barty hit 20 winners and saved six of seven break points to secure a 6-3 6-3 triumph and advance to a meeting with Danielle Collins after the American overcame Belinda Bencic 6-3 6-1.
Muguruza beat her fellow former world number one 3-6 6-3 6-4 after two hours and 19 minutes, having been one point away from falling 5-3 down in an entertaining decider at Foro Italico.
The 2016 French Open winner managed to hold her serve on that occasion, then broke to love in the next game before going on to seal the match at the third attempt.
"I think it was a tough match. I knew it was going to be a tough match. She's a good player, she's playing good, she's with a lot of confidence," said Muguruza.
"I knew it was going to be a tough battle. I was ready for it. I stood behind her and was waiting for my opportunities. She was playing great at the beginning. She took the first set. I kept myself together and said, 'Okay, let's start another battle in the second set'."
Next up for Muguruza is two-time Rome finalist Halep, who saw Yulia Putintseva retire from their quarter-final meeting due to a lower back injury.
After dropping her serve to fall 6-2 2-0 down to the world number two in 47 minutes, Putintseva, who played back-to-back three-set matches in the previous two rounds, pulled out of the match.
Halep said of Muguruza: "Every time I played well against her, [I was] as much as possible aggressive. If I play my best game and if I feel great physically on court, I have a big chance to win the match. But every time is different, because she's playing so hard.
"You don't really know what to expect. It's tough every time. So I don't plan for a specific match, because you never know on court."
Two-time Internazionali d'Italia champion Elina Svitolina was comprehensively beaten 6-3 6-0 by Marketa Vondrousova, who was the runner-up at last year's French Open.
Standing between Vondrousova and her first final appearance since Roland Garros last year is reigning champion Karolina Pliskova.
Second seed Pliskova overcame Elise Mertens 6-3 3-6 6-0 as she continued to impress after initially struggling when the WTA Tour returned in August.
