Roger Federer is doubtful for the US Open after he pulled out of the tune-up events in Toronto and Cincinnati with a knee injury.
Federer, who made a comeback from two knee surgeries, was last seen at Wimbledon. After battling though the first week, the 39-year-old seemed to run out of gas against Hubert Hurkacz.
The former Wimbledon champion went down 3-6, 6-7, 0-6 to the Polish youngster in the quarterfinals.
Federer has competed in five tournaments this year, recently missing the Tokyo Olympics due to injury.
When he announced his withdrawal from the Olympics, Federer tweeted: “During the grass-court season, I unfortunately experienced a setback with my knee.”
The World No. 9 made his Grand Slam comeback at French Open, where he reached the fourth round before withdrawing.
Federer has enjoyed success in Canada, winning two titles in Toronto, and is a record-holding seven-time champion in Cincinnati.
It was also announced Thursday that Tokyo Olympics singles gold medallist Alexander Zverev will not compete in Toronto.