Alexander Zverev is awaiting news on the true severity of his "very serious" ankle injury, with the world number three's Wimbledon participation in doubt.
The 25-year-old withdrew from Friday's French Open semi-final against Rafael Nadal after rolling his ankle towards the end of the second set, which went to a tie-break.
Zverev, who lost a gruelling first set 7-6 (10-8), was helped from the clay in a wheelchair before returning on crutches to retire, ending his hopes of a second grand slam final.
And the German is now in a race against time to be ready for the next major of the year, with Wimbledon set to begin in a little over three weeks' time.
Providing an update on his injury on social media on Friday, Zverev said: "It was a very difficult moment for me today on the court.
"It was obviously a fantastic match until what happened, happened. It looks like I have a very serious injury. But the medical team and the doctors are still checking on it."
Zverev made an ideal start to his semi-final against Nadal by breaking his opponent's service in the first game, but the Spaniard hit back in the eighth game of the opening set.
Nadal eventually edged a competitive tie-break to conclude a 91-minute set, and both men continued to exchange blows in a just-as-tight second set that also went the distance.
However, Zverev's injury brought what was shaping up to be a classic semi-final to an early end, meaning a 14th Roland Garros final for Nadal on what was his 36th birthday.
Casper Ruud awaits Nadal in Sunday's final in Paris in what will be the first encounter between the pair after overcoming Marin Cilic 3-6 6-4 6-2 6-2 in the other semi-final.
"I want to congratulate Rafa, obviously," Zverev added in his social media post.
"It's an incredible achievement, a 14th final, and hopefully he can go all the way and make some more history."