The injury is a blow to a team already looking for help on defense ahead of Feb. 29 trade deadline, but general manager Steve Yzerman told the Tampa Tribune that Garrison's loss won't affect their plans.
Tampa Bay could look to move Jonathan Drouin, a 2013 first-round pick who is suspended for refusing to report to Tampa's AHL affiliate and is seeking a trade, or team captain Steven Stamkos, who will be an unrestricted free agent after the season.
Garrison missed his first game of the season Tuesday. He has tallied four goals and three assists in 52 games in 2015-16, averaging 18:24 in ice time per game.
"He's a big part of our team and has been a big contributor for us ever since he's been here,'' Lightning coach Jon Cooper told the newspaper. "But it's part of the game; guys are going to get hurt. It's unfortunate for Gary, because he's been a rock back there for us. We'll just have to adjust, and somebody will have to fill in and take his place.''
The Lightning recalled defenseman Slater Koekkoek, their first-round pick in 2010, to fill Garrison's roster spot. Koekkoek has appeared in one game for the Lightning this season.
Information from ESPN staff writer Joe McDonald contributed to this report.