Rafael Nadal faced make-or-break tests on Thursday to determine whether he would have to abandon his Wimbledon campaign.
The 22-time grand slam winner aggravated an abdominal injury during his five-set victory over Taylor Fritz in the quarter-finals, admitting he had been in pain on court.
It did not prevent Nadal lasting the distance in a stirring battle lasting four hours and 21 minutes, taking the decider on a tie-break.
But Nadal risks having to pull out of Friday's semi-final against Australian Nick Kyrgios if his body is judged to have taken too much of a battering.
Family members appealed to Nadal to give up the ghost against Fritz, but the 36-year-old played on and pulled off a typically gutsy victory.
He confirmed after the match: "Tomorrow I'm going to have some more tests. But [it is] difficult to know. It's obvious that I am a player who had a lot of things in my tennis career, so I am used to have things and I am used to hold pain and to play with problems.
"Knowing that, when I feel something like I felt, that is because something is not going the proper way in abdominal. But let's see. I had these feelings for a couple of days."
Nadal said it was undoubtedly "the worst day" for his abdomen since he first felt a strain, which had required strapping before he played Fritz.
He said there had "been an important increase of pain and limitation", but Italian player Fabio Fognini appeared to question Nadal's injury status when he posted a message in an Instagram story, reacting to a report pointing out the Spaniard's problem.
The message read: "For sure... Guys stop believe in what you read PLEASE."
But Fognini later denied that meant he was questioning Nadal's injury, accusing journalists of twisting his words.
He wrote: "It's time to stop writing and reporting everything that you want in the wrong way. With that I wish Rafa and his entire team a lot of good luck in this Wimbledon final."
Former Spain goalkeeper Santiago Canizares, who now works in the sports media, also weighed in, writing on Twitter: "If there is anyone to believe in this society, it is @RafaelNadal. For many reasons that I am too lazy to cite.
"There are those who doubt his injury yesterday, but one fact does not bear debate: his serve was 30 per cent less than his usual speed ... Usual almost 200 km/h. Yesterday 150/160 km/h"
That did not quite stack up across the entire match, but Nadal's average serve speeds (107mph for first serve, 95mph for second serve) were his slowest of the tournament so far.
Nadal has already won the Australian Open and French Open titles this year, defying a long-time foot problem. Should he play on and win Wimbledon, he would go to the US Open in August with a chance of achieving the first men's singles calendar Grand Slam clean sweep since Rod Laver achieved the feat in 1969.
The winner of the semi-final between Nadal and Kyrgios, should it go ahead as planned, will face the winner of Novak Djokovic's match against Cameron Norrie in the title match.