Clijsters needed to have her thigh heavily strapped during the match
Kim Clijsters' preparations for defending her US Open title suffered a blow as she picked up a hip injury in defeat at the Rogers Cup in Montreal.
The Belgian lost 2-6 6-3 6-2 to Vera Zvonareva but later insisted she would be fit for Flushing Meadows.
"Don't worry, there's no doubt in my mind," said Clijsters.
"Maybe I will have to take precautions but a lot of girls these days play with tape to protect themselves. It doesn't mean you can't compete."
Zvonareva was merciless as she won nine games in a row to close in on her place in the last four.
Despite her plight Clijsters refused to quit and rallied at 0-5 in the third before Zvonareva broke serve to win.
"I don't like to give up," said Clijsters. "If something really bad happens, if you twist your ankle. But I was still able to move, still able to hit the ball, so I don't believe in giving up."
World number four Clijsters, who was unbeaten in seven outings on North American hard courts in the build-up to this match, had started strongly, breaking Zvonareva at the first time of asking to go 3-0 up.
Another break of serve saw her take the opening set but late in the second the injury kicked in, with Zvonareva twice breaking serve as she won the last four games of the set to level the match.
Clijsters received treatment during the changeover and later asked for a medical time-out, returning to the court with her left thigh heavily strapped.
Zvonareva's semi-final opponent will be 10th seed Victoria Azarenka, who edged to a 6-2 7-6 (8/6) win over Marion Bartoli.
On the other side of the draw, Svetlana Kuznetsova thrashed China's Zheng Jie 6-1 6-3 before world number two Caroline Wozniacki eased into the last four with an 6-3 6-2 victory over French Open champion Francesca Schiavone.
Wozniacki is likely to be the number one seed at the forthcoming US Open following the withdrawal of Serena Williams due to injury, and the 20-year-old Dane said: "It's something special to be the first seed at a Grand Slam but it doesn't really matter for me if I am first seed or second seed.
"It's just a number when you're on the court. I just want to beat every single one of the girls that are in my way, that will be my goal."