Georges St-Pierre, who vacated the UFC welterweight title after a controversial win over Johny Hendricks in November, has torn the anterior-cruciate ligament in his left knee during a training session.
The former mixed martial arts champion from Montreal tweeted about the injury. He also said that he'd return to training when he's recovered from surgery.
No word yet on when he plans to return to the octagon.
St-Pierre (25-2) said he needed to take some time off from UFC to concentrate on life outside the ring. Judging by posts on his Twitter feed, he's accomplished that as well as maintaining a rigorous training schedule.
UFC President Dana White said the injury is "terrible" for St-Pierre. "I feel for him."
White said he thought St-Pierre's planned layoff was going to be short, although the injury changes that time frame.
"I didn't think his hiatus was going to be that long," White said. "That's one of the risks you run when you get away from the sport like that. You have a small window as a professional athlete to make what you can. The guy gave up his belt, walked away from the sport, and now he's out for who knows how long ... last time he had this injury, it was 14 months."
St. Pierre sustained a torn ACL in his right knee in December 2011. He returned to the ring in November 2012, when he defeated Carlos Condit. His previous fight came in April 2011, when he beat Jake Shields.