BUFFALO, N.Y. -- Buffalo Sabres defenseman Mattias Samuelsson is out indefinitely with a lower-body injury, coach Lindy Ruff said Wednesday.

Ruff called the severity of the injury "pretty strong." He didn't specify the nature of the injury but said Samuelsson is not expected to need surgery.

Samuelsson was hurt in a 7-5 loss to Montreal on Monday, when a Canadiens player rolled up on his leg. It was Samuelsson's first game back after missing three as a healthy scratch in Ruff's bid to shake up his roster.

Ruff listed leading scorer Tage Thompson and goalie Ukko-Pekka Luukkonen as day-to-day, with both having an opportunity to play Thursday, when Buffalo hosts the St. Louis Blues. Thompson did not return to the game Monday after sustaining a lower-body injury.

Luukkonen started against Montreal despite dealing with what Ruff called an ailment, and he was pulled after allowing four goals on 18 shots through two periods.