Matteo Berrettini appeared to almost collapse during the second set of his defeat to Andy Murray at the Miami Open on Wednesday.
The Italian almost lost his balance as he was preparing to serve and had to be seen by doctors before resuming the first-round clash.
Berrettini won the first set 6-4 after breaking Murray in the first game of the match at Hard Rock Stadium in Florida.
But Murray fought back with a break of his own in the second set and was on the brink of levelling the match up at 1-1.
Mario Berrettini almost collapsed during his Miami Open match against Andy Murray
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Berrettini was set to serve at 5-2 down and bounced the ball in his usual setup on the baseline.
But he appeared to lose balance, using his racket to hold himself up as he almost fell to his right.
The 27-year-old clutched his head as he stumbled a couple of yards across the court.
The umpire made her way over to Berrettini to check on him and the medics were quick to attend by the side of the court.
Berrettini had his blood pressure taken as he also took on more fluids and energy supplements.
Former British No 1 Tim Henman was on co-commentary for Sky Sports and was shocked by the incident.
Henman said: "That was so unexpected. Berrettini has been playing good tennis and moving well, and all of a sudden looked extremely wobbly on his feet."
Annabel Croft also gave her verdict on the incident, claiming she thought Berrettini was 'going to faint'.
Croft said: "Very worrying scenes. Honestly I've never seen somebody look as if they were about to keel over.
"You wondered what was going on, I thought he was going to faint.
"He did well to steady himself and not crash to the surface, where he may have done some damage to his body or his head.
"It came over him so quickly. We've talked about the conditions, Laura [Robson] told us it hadn't been quite as hot as the qualifying, when another player nearly fainted, but it can suddenly happen."
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Matteo Berrettini was attended to by doctors during her match against Andy Murray
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Berrettini was deemed fit enough to continue and kept the second set alive, winning his next service game to love.
But Murray then saw out the set 6-3 to take it to a decider.
Henman still questioned whether Berrettini was in a condition to compete in the remainder of the match.
He said: "The question mark right now is Berrettini. He obviously had a bit of a strange turn at the end of that second set, feeling very dizzy on the court.
Matteo Berrettini had a medical timeout during his game against Andy Murray
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"How is he going to be able to perform in this third set? It was a very slow walk back to the court.
"By the looks of things, Murray is pretty eager.
"I do make Murray the favourite now. It was a really positive last few games for him when he got the break of serve."
Murray won the final set 6-4 to progress through to the second round.
On Monday, Arthur Cazaux was forced to pull out of his Miami Open qualifier against Harold Mayot after collapsing on court.