The Sabres announced Girgensons' injury upon returning to training camp Wednesday following a day off and said the timetable for recovery is about six months.
Girgensons, who is from Latvia, was preparing for his eighth season in Buffalo after being re-signed to a three-year, $6.6 million contract in October. Selected by the Sabres in the first round of the 2012 draft, he has developed into a dependable checking-line forward.
He had 12 goals and 19 points in 69 games last season. Overall, Girgensons has 61 goals and 138 points in 489 career games with the Sabres.
Buffalo, which opens the season by hosting Washington on Jan. 14, did receive some good news on Wednesday with captain Jack Eichel making his training camp debut after missing the first four days with a lower body injury. Goalie Linus Ullmark also practiced for the first time after completing his self-quarantine requirements.
The Sabres also added prospects Dylan Cozens and Jack Quinn to their training camp roster a day after the two represented Canada at the World Junior championship tournament in Edmonton, Alberta. Canada won the silver medal with a 2-0 loss to the United States on Tuesday.
It's unclear when the two will join the team.
Cozens, Buffalo's first-round pick in the 2019 draft, scored a tournament-leading eight goals and finished second with 16 points in seven games. The 19-year-old centre will be given an opportunity to compete for a spot with the Sabres while still being eligible to return to his Canadian junior team in Lethbridge, Alberta.
Quinn, selected with the No. 8 pick in October, had a goal and four assists in seven games at the world juniors. The 19-year-old right wing is still eligible to return to his Canadian junior team in Ottawa.