Boston Celtics star Jayson Tatum admitted he is still battling with the after-effects of coronavirus despite returning to NBA action three weeks ago.

Speaking ahead of Boston's 112-99 win over the Denver Nuggets on Tuesday, where Tatum contributed 21 points, six rebounds and eight assists, the All-Star revealed he was still experiencing respiratory issues during games.

Tatum tested positive for COVID-19 in early January, alongside some team-mates, forcing three Boston games to be postponed.

"I think it messes with your breathing a little bit," Tatum told reporters.

"I have experienced some games where, I don't want to say struggling to breathe, but you get fatigued a lot quicker than normal. Just running up and down the court a few times, it's easier to get out of breath or tired a lot faster; I've noticed that since I've had COVID.

"It's just something I'm working on. It's gotten better since the first game I played, but I still deal with it from time to time."

The Celtics have a 7-10 record since then, slipping to third in the Atlantic Division of the Eastern Conference, behind the Philadelphia 76ers and Brooklyn Nets.

After a period of quarantine, Tatum returned to the court with 24 points against the Chicago Bulls on January 25.

Tatum has not missed any of Boston's 12 matches since returning, top scoring for the Celtics on seven occasions, insisting the issues have not affected his performances or output.

"It's gotten better obviously from the first game I came back and played, but I guess it's just a long process," he said.

"I've talked to other guys that have had it and they say they experienced the same thing and it kind of just gets better over time. But as much as we play, I guess it takes a little bit longer.

"You've got to take it on the chin when things aren't going great and you're not playing how you should be."

World number one Ash Barty refused to criticise Karolina Muchova's reasoning for a medical timeout after she was surprisingly beaten in the Australian Open quarter-finals.

Barty's bid to become the first Australian woman to win the Melbourne grand slam since 1978 came to a shock end on Wednesday, upstaged by 25th seed Muchova 1-6 6-3 6-2.

Winner of the 2019 French Open, Barty raced through the opening set in 24 minutes and led 2-1 in the second before Muchova requested an off-court medical timeout on Rod Laver Arena.

It was a turning point, Muchova returning reinvigorated as the unheralded Czech reached her maiden major semi-final in remarkable fashion, with the 24-year-old revealing during her on-court interview, "I was a bit lost [gestures at head] on the court and my head was spinning so I took a break. It helped me.

"It was more they just checked my pressure because I was a bit lost. I was spinning. So they cooled me down a bit with ice and it helped me."

Asked about Muchova's actions, Barty told reporters: "It's within the rules. She's within her rights to take that time. If she wasn't within the rules, the physios and the doctors would have said so. That's the laws of our game, is that we have those medical timeouts for cases that are needed. Obviously she needed that today. Completely within the rules for her to take that.

"From my point of view, I've played a lot of matches where there have been medical timeouts. I've taken medical timeouts myself before, so that shouldn't be a massive turning point in the match. I was disappointed that I let that become a turning point. I'm experienced enough now to be able to deal with that. It's a disappointment today without a doubt. But we learn and we move on."

Barty added: "I would have liked to have just been a little bit sharper the next game. Started well with the first point, just made a couple loose errors in that game. I think for the rest of the set, that was the story, it was just over and over-made. Probably pressed a little bit trying to be overly aggressive.

"Had some break points, I think it was that three-all, that was probably a bit of a critical game in the momentum there for the second set. Just disappointed with the fact that I wasn't able to bring the match back on my terms after she took that break."

"I didn't hear what she said when she called for the trainer," Barty continued. "That's not my decision. When you call for the trainer, you obviously tell the umpire what the reason is. And then the doctor and physios come out and assess it. That's within the rules. For me, that's not really my decision and not my concern what she took the medical for.

"Obviously there are rules when we go off the court for whatever areas you're getting treated because that's quite normal. But, yeah, that's not really my decision to make on whether or what her medical condition was or what the timeout was for."

Brady, who tallied 31 unforced errors in the final two sets having only managed six in the first, said: "It's heartbreaking, of course. But will it deter me, will it ruin the fact we've had a really successful start to our season? Absolutely not.

"The sun will come up tomorrow. We go about our work again. You're either winning or you're learning. I think today is a massive learning curve for me, for Tyz [coach Craig Tyzzer], my team as well. We take the positives out of it, without doubt and don't let this particular match, this particular hour of tennis deter us from what we're trying to do."

Australian Open fans are set to return to Melbourne Park from Thursday after the Victorian government confirmed the lifting of restrictions following a five-day lockdown amid the coronavirus pandemic.

While the number of supporters set to attend remains unknown, fans will be back in their seats for the beginning of the Australian Open semi-finals, with record-chasing Serena Williams set to face three-time grand slam champion Naomi Osaka in Melbourne.

Defending men's champion Novak Djokovic will play the tournament’s surprise package, Russian qualifier Aslan Karatsev - who is the first player to reach a semi-final on their grand slam debut.

Djokovic was on court when the lockdown came into effect last Friday, with the five-day "circuit-breaker" designed to control an outbreak of the UK coronavirus strain.

Part of the third round, the fourth round and quarter-finals of singles action were played behind closed doors after a series of outbreaks in Victoria.

The state has recorded 12 more active cases since the lockdown was implemented but, with none discovered in the past 24 hours, Victorian premier Daniel Andrews announced restrictions will be eased.

"I'm very, very pleased to announce that the restrictions will come off, almost all of them, at midnight tonight," Andrews told reporters on Wednesday.

"From 11:59pm [Wednesday local time], the restrictions will be dropped [but] masks will be required indoors and outdoors when you can't socially distance."

The stage-four restrictions meant residents could not leave their homes for any other reason than work, shopping for groceries, exercise or the giving or receiving of medial care.

This year's delayed Australian Open has had crowds capped at 30,000 per day with original COVID-19 restrictions, but new limits are yet to be determined for the rest of the tournament.

"There will be meetings this afternoon [to determine] what is a safe number," Andrews said.

"They already were reduced, they may have to be reduced further, but that matter will be resolved in the next few hours."

Liverpool took charge of their Champions League last-16 tie with RB Leipzig as they claimed a 2-0 win in the first leg in Budapest.

Julian Nagelsmann's side, who pipped Manchester United to a place in the knockouts, looked far from comfortable in the unfamiliar surroundings of the Puskas Arena, where Tuesday's game was held to due to coronavirus travel restrictions.

Mohamed Salah's 24th goal of the season put Liverpool ahead after a mistake by Kevin Kampl, and Sadio Mane doubled the advantage when Nordi Mukiele gifted him an opportunity.

The Reds are now unbeaten in six away games against Bundesliga opposition stretching back to 2002, and Jurgen Klopp's men will be firm favourites to progress to the quarter-finals.

Liverpool nearly fell behind after just five minutes, Dani Olmo's diving header hitting the inside of the post from Angelino's cross.

The away side looked the most threatening as they began to take control, and Peter Gulacsi was alert to block a Salah effort from close range before Roberto Firmino fired a shot into the side-netting.

Mane then headed over from six yards from a Firmino cross, and the Senegalese thought he had set up his strike partner to nod in the opener after errors from Dayot Upamecano, but the ball had gone out of play.

Christopher Nkunku had barely been involved in the first half but he could have given Leipzig the lead early in the second, Alisson saving well after the striker ran onto Olmo's throughball.

It was Salah who broke the deadlock 53 minutes in, drilling past Gulacsi after a dreadful backpass from Kampl, and it soon got worse for Leipzig.

Mukiele made a complete mess of a simple clearance forward by Curtis Jones, and Mane had time to stride into the box and slot home.

Angelino had a chance to pull a goal back but sliced his attempt badly, summing up a poor game for last season's semi-finalists.

What does it mean? Fragile Liverpool give season huge boost

Injuries and recent form - they had won three of their previous 12 games in all competitions - will have had Liverpool fans feeling a little anxious before meeting the side second in the Bundesliga.

However, a display of supreme authority, helped by an erratic approach from Leipzig, put Klopp's men in total charge of this tie and could well have provided a timely boost in confidence.

Leipzig will hope for better in the second leg, but their previous visit to England ended in a 5-0 defeat to Manchester United.

Salah at menacing best

Salah should perhaps have scored sooner but he made no mistake with his clearest chance of the game.

He spent the rest of the game harassing a deeply unsettled Leipzig defence in a hugely impressive, committed performance.

Nagelsmann's men in a muddle

Leipzig were on a six-game unbeaten run at home in this competition and it was unfortunate for them that this game had to be relocated to a neutral venue.

Still, that does not explain the horribly haphazard nature of their performance. Two defensive errors led directly to the goals, Mukiele could have been sent off before his mistake, while Bayern Munich-bound Upamecano misplaced 20 passes from centre-back.

What's next?

With the return leg not until March 10, Liverpool's more pressing concern is a derby with Everton on Saturday. Leipzig head to Hertha Berlin in the Bundesliga a day later.

Joao Felix is back in contention for Atletico Madrid after being sidelined with coronavirus, Diego Simeone has confirmed.

It was confirmed Portugal international Joao Felix tested positive for the virus on February 3, forcing him to miss two games for LaLiga's leaders.

The first was a 2-2 draw at home to Celta Vigo, who netted a late equaliser, before Atleti beat Granada 2-1 in Andalusia on Saturday to stay five points clear at the summit with two games in hand on second-placed Real Madrid.

Moussa Dembele, Thomas Lemar and Hector Herrera were all confirmed as having the virus in the five days after Joao Felix's results were returned, but the situation has had minimal impact on the team's on-field performances.

Up next is a trip to Levante on Wednesday, before hosting Paco Lopez's men at the weekend, and that is followed by the first leg of their Champions League last-16 tie with Chelsea.

Simeone is unsure if Joao Felix will feature on Wednesday but was glad to have him back.

"He has not had many symptoms that left him unable to train at home, so he was working with the coaches since the fourth day [of his absence]," Simeone told reporters.

"He is eager and enthusiastic, he is healthy. It's great to be able to count on him tomorrow, but we will decide tomorrow what to do with him."

Attention soon turned to Atletico's other key attacker this term, Luis Suarez, who has recently been the subject of reports claiming the Uruguayan has a clause in his contract that would allow him to leave on a free transfer at the end of the season.

Simeone seemed unimpressed he was even asked the question.

"Normally I don't talk about personal contracts," Simeone said.

"I talk about how to attack, how to play, but I don't interfere in personal matters."

Ben Simmons believes his potential is "scary" after scoring a career-high 42 points against the Utah Jazz.

Playing at center in the absence of Joel Embiid for the Philadelphia 76ers, Simmons converted 15 of his 26 field goals, adding 12 assists and nine rebounds in a fantastic performance.

Utah still won the game 134-123 to make it 19 wins from 20.

Despite playing in a third straight loss, Simmons believes the record night shows he has made huge strides over recent weeks.

"I feel like I'm figuring it out," Simmons said after the game.

"Obviously, my scoring has been a lot higher the past five, six games.

"As long as I can keep doing that and stay locked in and keep working on my mental [game], I think it's scary.

"You have got to keep your foot down. Keep pushing forward offensively with me. Stay dominant - I know what I'm capable of.

"It felt good that I was able to dominate offensively. Defensively I did okay, not great. Offensively, I definitely had to pick up the slack especially if Joel is out. So yes [it was probably my most aggressive game].

"I loved when I saw Rudy [Gobert] was guarding me. I love being able to go at somebody like that. I felt like it was a little bit disrespectful to put him on me, but it is what it is.

"Honestly, I've just been working on my mentality and mental [game] a lot these past few weeks.

"It's not easy to do that. Your mindset will change the way you play or certain things in the game that come natural for certain people. It is all mental.

"People don't realise your mentality is a huge part of the game. For me I continue to work on that. I'm just trying to get better and progress my game and get to that next level.

"But we wanted to get this win bad. We didn't get it, so we've got to move on."

Getting Simmons matched up with Gobert was exactly what coach Doc Rivers had in mind, while he also praised Tobias Harris for a 36-point display.

Rivers said: "I didn't know we were going to get the 42 points out of him! But he did everything - he guarded, did a good job. Played with pace.

"We anticipated once Joel scratched that the lineup that we put on the floor, we were trying to create a lineup where Gobert would guard Ben and that happened.

"The key for us was getting stops and getting it to Ben and getting up the floor. We just felt like there was no way anybody was going to stay with Ben, especially a center.

"Tobias [Harris] was phenomenal as well. Look at those two guys, man!

"Harris has to be straight line, aggressive and powerful. When he plays like that, he's hard to deal with. He played a very decisive game and had very few indecisive plays.

"He is really keeping the game simple, playing with great force, scoring from the three[-point line], off the dribble and the post. He's doing exactly what we believe he can do.

"[Embiid] was just a late scratch. They came to me and told me his back is still stiff. So I don't think this is a long term issue or anything like that. It's just a game missed."

The Sixers are still top of the Eastern Conference at 18-10 and host the Houston Rockets next on Wednesday.

Jordan Clarkson scored 40 points off the bench for the impressive Jazz, who lead the Western Conference with an NBA-best record of 23-5.

Novak Djokovic lost his temper but refused to let the prospect of Australian Open glory slip away as he edged out Alexander Zverev to reach the semi-finals.

The world number one destroyed a racket when trailing 3-1 in the third set, after he and Zverev split the opening two sets, and it was one of a number of moments when the Serbian showed heightened volatility during a 6-7 (6-8) 6-2 6-4 7-6 (8-6) win.

Still bothered by an abdominal problem that he sustained in the third round, Djokovic nevertheless strides on and will face Russian qualifier Aslan Karatsev for a place in the final.

Zverev, who played in a bright yellow headband and vest top, with a gold medallion hanging from his neck, will look back on an opportunity missed.

As well as that third-set lead, Zverev was also up a break at the start of the fourth, but the US Open runner-up lacked the composure to convert those hard-earned positions.

If Djokovic's racket-smashing was a tactical move designed to gee himself up and distract Zverev, then it worked a treat.

A nip-and-tuck opener had gone the way of German world number seven Zverev, who then made a wretched start to the second set and was 4-0 behind in the blink of an eye.

Just as momentum began to swing back Zverev's way in the third, Djokovic went into his rage, with a ball girl summoned to clear up the mess the 33-year-old created.

Back came Djokovic as double faults began to leak from Zverev's racket, and soon they were into a fourth set.

Zverev led 3-0 but Djokovic was not going away, seizing on mistakes from an opponent who by the end of the second tie-break of the match could only wonder what might have been.

An ace from Djokovic finished off the contest. After eight titles at Melbourne Park, a hunger for more continues to define his every performance in Australia.

"Emotionally I feel a little bit drained. We pushed each other to the limit," Djokovic said in his on-court interview.

"Other than in the second set I started pretty poorly in all the other three sets. I lost my service very early in the first, third and fourth and allowed him to swing through the ball a bit more, but I regained my focus.

"I broke that racket and things started to shift a little bit for me in a positive direction."

Aslan Karatsev said finding stability off the court has helped him become the revelation of this year's Australian Open after the qualifier marched on to the semi-finals.

The Russian became the first qualifier to reach the last four of a major since Vladimir Voltchkov, famously in borrowed shorts, did so in 2000 at Wimbledon.

It was Pete Sampras who eventually blew away Voltchkov's threat at the All England Club on his way to another title.

And it turns out there is a connection between Karatsev and Voltchkov, with both men now calling Minsk their home.

But whereas Voltchkov is Minsk born and bred, Karatsev has taken a roundabout route to setting down roots in the capital of Belarus.

He explained on Tuesday how he was born in the Russian city of Vladikavkaz before moving as a toddler to Israel with his family and living there until the age of 12, when he and his father returned to Russia, spending time in the city of Taganrog.

Tennis took him to training bases in Moscow, then Halle in Germany, Barcelona, and finally Minsk.

It is in Minsk that Karatsev has linked up with former ATP professional Yahor Yatsyk, a man only one year his senior but already settling into coaching.

As Grigor Dimitrov succumbed to injury and slid to a four-set defeat against Karatsev on Tuesday, the unlikely figure in the final four reflected on his long road to this point.

"Yes, I was moving I would say too much," Karatsev said of his nomadic existence.

"In the end I found a coach, Yahor Yatsyk, and this is the right guy for me. He's helped me a lot, more the mental part, and then of course there is the technical stuff as well.

"I like to work with him. We're living in Minsk. We're practicing there."

Karatsev is the lowest-ranked man to reach a grand slam semi-final since Goran Ivanisevic, who won Wimbledon in 2001 on a wildcard entry while ranked 125th in the world.

His charge through the draw makes him only the second qualifier to advance to the Australian Open last four, after Bob Giltinan in December 1977.

"Of course it's amazing that I passed to the semi-finals from qualifying," Karatsev said. "I'm just trying to enjoy the moment and not thinking about that too much and playing from round to round."

He and Yatsyk set the goal of reaching the top 100, which Karatsev had not managed before getting to Melbourne.

Before this fortnight he stood at 114th in the rankings, but he will hurtle to a double-digit ranking next week.

"I think the key is to find the right team, the right coach that I found. I was really lucky to find him," Karatsev said.

"We just met in one tournament. We were saying, 'Okay, let's try to work together', and it's really a big luck that we started to work together and I have a good team around me."

Before he encountered Yatsyk, who as a player did not crack the top 1,000 in singles, Karatsev had a brief moment when he wondered if he might not make the grade.

"There was a time when I was injured that was a difficult time for me because I recovered after the injury, and then 2017 started, and I started to play again, and again I felt the knee," Karatsev said. "I said, 'Whoa.' I quit again for two and a half months, almost three, and I think this is the most difficult part."

Mason Greenwood has signed a new contract at Manchester United that ties him to the Premier League giants until June 2025.

Mason Greenwood has signed a new contract at Manchester United that ties him to the Premier League giants until June 2025.

United said the deal includes the option for a further year, emphasising their belief that academy product Greenwood, 19, is poised to play a big part in their future.

The teenage forward has emerged among Europe's leading players in his age group, having made his debut as a 17-year-old and been a regular within the first-team squad ever since.

Manager Ole Gunnar Solskjaer said Greenwood, who joined United's youth system as a seven-year-old, is primed to be a big part of the team in years to come.

"Mason is a fantastic talent and yet another fine example of the type of player that our academy produces," Solskjaer said. 

"He has made great progress this season, showing real maturity and adaptability to his game, which has seen him develop into one of the best young players in the country."

Solskjaer believes Greenwood, who has scored just once in 18 Premier League appearances this season, has boundless scope for improvement in his game.

The United boss told the club's website: "Whilst it is easy for people outside of the club to forget that Mason is just 19, it is our job as coaches to ensure he reaches his phenomenal potential and every step we take is to help him along that path.

"Mason is naturally gifted and has a brilliant attitude; we know how important he is going to be for Manchester United over the coming seasons."

Greenwood's previous deal, signed in October 2019, would have taken him through to the end of the 2022-23 season.

Now, along with the likes of Marcus Rashford, he looks like being a long-term piece of United's first-team dressing room.

Greenwood, who has one England cap, said: "I've worked so hard to reach this level and the last two years have been amazing. 

"There is so much that I want to achieve in the game and I know that this is the perfect environment to play my football.

"With the support from the manager, his coaching staff and so many great players to learn from; I know that I am developing every single day. 

"There is a lot more to come from myself and this team and I am so committed to working hard week in, week out to help the group achieve success.

"I want to repay the club for the support that everyone has given me over the years and show everyone just what I am capable of."

France had their Six Nations plans disrupted by a positive COVID-19 test that sent the squad into self-isolation on Tuesday.

The French Rugby Federation (FFR) also said head coach Fabien Galthie would be retested amid concerns he may have coronavirus.

It was another figure from within the France camp, who was not named, that returned a positive result following testing on Monday.

Announcing that news, the FFR said on Tuesday: "Following the PCR tests carried out last night in Marcoussis with the France XV, all the players tested negative, a member of the technical staff tested positive, as well as a suspicious and unproven case concerning Fabien Galthie who will be tested again this morning.

"In accordance with health protocol, all members of the team and management were isolated this morning. Interactions are kept to a minimum.

"An additional test at the National Rugby Centre will be carried out on Wednesday morning for the entire squad."

The squad are due to disperse later this week to be allowed a short time at home between matches, with France, who have won their opening two games, not in action again until they face Scotland on February 28 in Paris.

They scored a fine 15-13 win over Ireland in Dublin on Sunday to follow up the opening 50-10 victory over Italy.

The FFR statement added: "Tests will be carried out at home on Friday, as well as on Sunday evening at the National Rugby Centre when the squad reunites.

"The announcement of the 31 players for the Scotland match will take place this Wednesday evening, February 17."