Marcus Pettersson was placed on long-term injured reserve retroactive to March 18 with a lower-body injury.
The defenseman is week to week after leaving at 3:51 of the third period in a 6-0 loss to the New York Rangers on Saturday.
Pittsburgh will be without Pettersson, and defensemen Jeff Petry, Jan Rutta and Dmitry Kulikov, when it tries to end a three-game losing streak against the Ottawa Senators at PPG Paints Arena on Monday (7 p.m. ET; SNE, SNO, SNW, ATTSN-PT, RDS, ESPN+, SN NOW).
"I think we can rally around this," coach Mike Sullivan said. "It's a great opportunity for some guys to step up and play some more significant roles back there. It's a great opportunity for all the rest of us to make sure we play an inspired game, a spirited game."
Petry is day to day with an upper-body injury and will miss a second straight game; Rutta did not play Saturday with a lower-body injury that has him week to week. Kulikov is also week to week with a lower-body injury sustained March 12.
"I think you have to be a little more desperate and understand that simplifying things becomes more important," Penguins captain Sidney Crosby said. "You know guys will be playing different roles and different minutes. You just want to make sure you're helping each other."
Pettersson, who has 24 points (one goal, 23 assists) in 67 games, was on the top defense pair with Kris Letang on Saturday. Pierre-Olivier Joseph will likely take his place against Ottawa.
Taylor Fedun worked on a third defense pair with Mark Friedman during the morning skate after being recalled on an emergency basis from Wilkes-Barre/Scranton of the American Hockey League on Monday. -- Wes Crosby