Kotalik hurt the knee colliding with Boston defenseman Andrew Ference five minutes into the second period in Buffalo's 4-3 shootout loss to the Bruins on Saturday.
Kotalik's name is added to a growing list of banged-up Sabres. Buffalo is now down six regulars after Maxim Afinogenov, the team's second-leading scorer, broke his left hand and Jiri Novotny twisted his left ankle in a 2-1 overtime win over Edmonton on Thursday. Afinogenov is expected to miss a minimum of six weeks, while Novotny will be out indefinitely.
Buffalo has already lost forward Paul Gaustad (torn tendon) for the season, and defenseman Jaroslav Spacek (broken left hand) will be out for about a month. Center Tim Connolly has yet to play this year after sustaining a concussion in last season's playoffs.
Kotalik has 14 goals and 36 points in 59 games this season after setting career highs in goals (25) and points (62) last year.
To replace Kotalik, Buffalo recalled Michael Ryan from AHL Rochester. Ryan has played in three games for the Sabres this season, failing to register a point.
Buffalo (39-15-5) leads the league with 83 points, and will host Philadelphia on Tuesday.