Doha - World number five Dominic Thiem dramatically pulled out of the Qatar Open because of illness on Friday just hours before he was due on court to play his semi-final.
In an official statement, Thiem said he had flu and a "very high fever".
The tournament's number one seed was due to play Frenchman Gael Monfils on Friday evening in Doha.
Instead, wildcard Monfils will proceed straight to Saturday's final.
"It is highly regrettable that I won't be able to play the semi-final match against Gael," said Thiem.
"As much as I would have loved to honour the match but the current status of my health wouldn't permit me.
"I'm down with flu and I hope to recover as soon as possible.
"I thank my fans and the organisers for their support."
The 24-year-old Austrian was the only seed left in the competition and had yet to drop a set on his way to the last four.
He had beaten Evgeny Donskoy, Aljaz Bedene and Stefanos Tsitsipas in straight sets.
Monfils, the last non-seed to appear in a Qatar Open final, will play either Andrey Rublev or Guido Pella on Saturday.
The Russian and Argentinian play later on Friday.
It is the latest blow to this year's tournament in Doha, which was shorn of three major stars before it even began, with Novak Djokovic, Stan Wawrinka and Jo-Wilfried Tsonga pulling out as they try to recover from injuries.
Qatar Open results on Friday (x denotes seeding):
Gael Monfils (FRA) bt Dominic Thiem (AUT x1) - walkover