Former UFC welterweight champion Georges St-Pierre tweeted out that he suffered a torn ACL in training and will undergo surgery in the coming days.
St-Pierre vacated his title last year after defeating Johny Hendricks, citing a need to get away from MMA for now.
GSP has not officially retired, and UFC president Dana White has stated he believes the Canadian will return sooner rather than later.
Hendricks won the vacant title from Robbie Lawler earlier this month via decision.
Tore my left ACL in training. Surgery in a few days. Rehab, pain, hard work, no shortcuts- I'll soon be back at 100%. Thanks for the support
— Georges St-Pierre (@GeorgesStPierre) March 27, 2014