BUFFALO -- Rasmus Dahlin will be out indefinitely for the Buffalo Sabres because of a concussion.

The defenseman was injured on a hit by Tampa Bay Lightning defenseman Erik Cernak in a 5-2 loss Monday. Cernak was suspended two games.

Dahlin, the No. 1 pick by Buffalo in the 2018 NHL Draft, has 16 points (one goal, 15 assists) in 24 games this season. He had 44 points (nine goals, 35 assists) in 82 games in his rookie season in 2018-19 when he was a finalist for the Calder Trophy given to the NHL's best rookie.

Sabres center Vladimir Sobotka is also out indefinitely after he had surgery on his right knee Tuesday. He has not played since he was injured on a hit by Lightning forward Nikita Kucherov in the first period of a 3-2 loss at the 2019 NHL Global Series in Stockholm on Nov. 8.

"It is long-term. I never like to bookend an injury of that nature," coach Ralph Krueger said. "Let's work with him and do everything we can and try to get him back but it's definitely long-term.

Video: Erik Cernak suspended two games for elbowing

"We're really sad about it. [Sobotka] was an amazing leader in how we want to play here. He was an example on video over and over again of playing the right way without the puck. We'll tap into him to help mentor some of the younger players here as he's injured and use his wealth of experience in that way."

Sobotka has three points (one goal, two assists) in 16 games this season. A fourth-round pick (No. 106) of the Boston Bruins in the 2005 NHL Draft, he has 171 points (53 goals, 118 assists) in 548 NHL games through 11 seasons with the Bruins, St. Louis Blues and Sabres.

The Sabres are also without forward Evan Rodrigues, who is week to week with a lower-body injury sustained in a 5-2 win at the Florida Panthers on Sunday. Forward Kyle Okposo (concussion) and center Tage Thompson (upper body) are also out long-term.

"It's frustrating. You don't want to lose guys to injury at all," captain Jack Eichel said. "It's part of this game, it's a physical game, it's a long grueling season, and it takes a toll on people. We're not the only team that's dealing with injuries. We've just got to find a way to get through it."

The Sabres (11-10-3) host the Calgary Flames at KeyBank Center on Wednesday (7 p.m. ET; MSG-B, SNW, NHL.TV).