Letang (upper body) and Dumoulin (concussion), who normally make up Pittsburgh's top defense pair, are progressing but haven't started skating. Maatta is out indefinitely with an upper-body injury sustained Feb. 11.
Rust is out longer-term with a lower-body injury sustained in a 5-2 win against the Columbus Blue Jackets on Tuesday. Ruhwedel is also longer-term because of an upper-body injury sustained in that game.
Despite the injuries, the Penguins hold the second wild card into the Stanley Cup Playoffs from the Eastern Conference, one point ahead of the Blue Jackets. They are tied in points (74) with the Carolina Hurricanes for third in the Metropolitan Division.
Defenseman Erik Gudbranson hopes to help keep Pittsburgh in a playoff position when he debuts Friday after being acquired in a trade with the Vancouver Canucks for forward Tanner Pearson on Monday. The 27-year-old practiced with the Penguins for the first time Wednesday and skated on the second pair with Marcus Pettersson.
Being thrust into a vital role is something Gudbranson welcomes, even if it comes with several of his new teammates injured.
"It's unfortunate, but fortunate I kind of get thrown into it really quickly here," Gudbranson said. "Not necessarily getting my feet wet, I'm really diving in. So I'm excited for the upcoming game and I'm ready to get going."
Gudbranson had eight points (two goals, six assists) and was minus-27 in 57 games with Vancouver this season. He admitted he was disappointed with how he's performed, but Sullivan expects him to help make up for the loss of some key defensemen.
"We're excited to have him," Sullivan said. "He's going to bring a physical element to our blue line. He's got good size. He's strong. He'll be strong in the battle areas, he'll be strong at the net front. He brings an edginess to his game that we know is going to help our whole overall group."
Replacing Rust, who played third-line right wing Tuesday but has skated on first-line center Sidney Crosby's wing at various points this season, could be more complicated. The Penguins will likely recall a forward from Wilkes-Barre/Scranton of the American Hockey League to fill out the lineup.
Whoever gets the nod likely won't replace the 17 goals Rust has scored this season, but Sullivan thinks there's no point in focusing on that.
"[Rust] is a good player for us," Sullivan said. "He brings a lot. He's a good penalty killer. His speed, he brings so much speed and puck pursuit to the lines that he plays on. But it's just part of the game."
