Letang was injured three minutes into the Penguins' 6-3 loss to the Detroit Red Wings at Joe Louis Arena on Saturday. Letang got tangled up with Red Wings forward Thomas Vanek, spun around and fell down, and went to the locker room. He returned a few minutes later but left the game for good after one shift.

Letang was placed on injured reserve Monday. His average ice time of 25:12 leads the Penguins but he's missed seven games with a lower-body injury and five games with an upper-body injury.

"Obviously he's a hard guy to replace," Sullivan told the Penguins website after the game. "He's our top defenseman, but we've done it before. He's been out before. We've got capable people. It won't be any one guy -- it'll be by committee. Let's not get ahead of ourselves. We'll see how he is."

Video: NHL Tonight: Injury Updates

Forward Jake Guentzel and defenseman Chad Ruhwedel were recalled from Wilkes-Barre/Scranton of the American Hockey League.

The Penguins (26-11-5) have scored six goals in a three-game losing streak entering their game against the Washington Capitals at PPG Paints Arena on Monday (7 p.m. ET; NBCSN, SN, TVA Sports, ROOT, NHL.TV). They are tied with the New York Rangers for third place in the Metropolitan Division and six points behind the Capitals, who have won nine straight.