The forward left during the first period of a 4-3 loss to the Montreal Canadiens on Wednesday after a check against Canadiens defenseman Shea Weber.
"'Kass' is a good player," Oilers coach Dave Tippett said Saturday. "He's a player that's built for playoff-style games and we're certainly going to miss him. Hopefully, he can heal up quick and we'll see where it gets to in the next few weeks."
Kassian has scored five points (two goals, three assists) in 27 games this season and is fourth among Oilers forwards with 73 hits.
Goalie Mike Smith left practice early Saturday with an apparent injury, but Tippett said it was not serious.
"He just tweaked something," Tippett said. "He's all right. I went in and saw him and he's fine now. It scared him a little bit, but he went and got it checked out."
Edmonton (27-16-2) is third in the seven-team Scotia North Division, one point behind the second-place Winnipeg Jets and seven ahead of the fourth-place Montreal Canadiens. The top four teams will qualify for the Stanley Cup Playoffs.
The Oilers are scheduled to visit the Jets on Monday.
