World No. 1 Lee Chong Wei's Olympic gold-medal quest was in doubt after he twisted his right ankle and pulled out of the Thomas Cup on Tuesday.
Lee was leading Denmark's Peter Gade 2-1 in the first game when the injury occurred while he was retrieving the shuttle on the baseline. He was led off the court in a wheelchair and taken to hospital for scans.
Badminton Association of Malaysia general manager Kenny Goh said it was too early to say how bad the injury was.
"These things do happen in badminton and no one can predict how it will pan out," Goh said. "We are disappointed and we hope the injury will not be as bad as it looked."
Gade, who's Denmark team went on to beat Malaysia 3-2, said, "He twisted his ankle, and I knew immediately that it was pretty serious," Gade said.
"This is for sure not the way I wanted to win a match.”