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 proceeds straight to Saturday's final.
There he will meet rising Russian star Andrey Rublev, who saved a match point before beating Argentina's Guido Pella 6-2, 4-6, 7-6 (7/2).
"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."
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.
He had been as impressive as Rublev who hit 40 winners and saved one match point in the tenth game of the final set on Friday to secure his place in the final.
It will be the Russian's third career final.
The 20-year-old is the current world number 39 but his ranking will rise to at least 33 after Doha and will be seeded at the Australian Open in only his second appearance in Melbourne because of injuries to other players.
"I am very happy, I don't even know what to say because I didn't expect this result," said Rublev.
On the match point he saved, Rublev added: "I was thinking before match point that I had to go for the shot, to go for the serve. In the end I got lucky."
Monfils will be appearing in his fourth Doha title match having lost all the previous three.
The 31-year-old first made the final back in 2006, where he was defeated by Roger Federer in straight sets.
Saturday's final will be the first between two non-seeded players in Doha since 2004, when Ivan Ljubicic beat Nicolas Escude.
It will also be the first time Rublev and Monfils have played against each other.
The absence of Thiem 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):
Semi-finals
Gael Monfils (FRA) bt Dominic Thiem (AUT x1) - walkover
Andrey Rublev (RUS) bt Guido Pella (ARG) 6-2, 4-6, 7-6 (7/2)
