Malkin, the league's reigning MVP, has played three games in the past three-plus weeks due to a concussion and his current upper-body injury. He has resumed skating but remains out indefinitely.
Potentially joining Malkin on the injured list is Letang, who suffered a lower-body injury in the first period of Sunday's 2-1 win over Boston. After losing their second-leading assist man, the Penguins (22-8-0) again relied on their rejuvenated defense and earned a seventh straight home win despite getting outshot 32-18 - 12-3 in the final period.
Pittsburgh has allowed five goals over its last five games after giving up 37 in its previous nine.
"Our team defense has been a focus for us and how we play, and it's everybody," coach Dan Bylsma said. "The responsibilities of our forwards in the defensive zone has been a key for us both offensively and defensively. In the defensive zone we're six guys defending there."
"It seems like it's always different guys, so that's what you need in order to have success consistently. We've been getting that lately," Crosby said. "Our depth is a big part of our success. We need to continue to show that."
The Penguins have shown their superiority over the Capitals in two matchups this season. During a 6-3 victory in Washington on Feb. 3, Chris Kunitz became the first Penguin to score four goals in a game since Jaromir Jagr on Oct. 14, 2000, and Crosby assisted on three of those scores.
Crosby and Malkin each had three points in a 5-2 home win over the Capitals four days later. The Penguins have taken three straight in the series and won back-to-back home matchups after losing eight in a row there in the regular season.
Instead of facing a fellow Eastern Conference contender, Pittsburgh will take on a team that's near the bottom of the standings. The normally competitive Capitals haven't helped themselves with a 4-8-1 road record, but they have won two of three overall after losing three in a row.
Washington (12-15-1) pulled away with three second-period goals in a 5-3 victory over Buffalo on Sunday.
"We need to win every day," said captain Alex Ovechkin, who scored his second goal in three games. "This kind of situation, you have to do everything you can, game by game."
Ovechkin has a team-best 11 goals but will likely need to go on a scoring binge to keep his seven-season streak of 30 or more going past this lockout-shortened campaign. His 39 career points against Pittsburgh are his second-most versus any team outside the Southeast Division, and he has two goals and four assists in the past three matchups.
The loss of Malkin could hurt as he had two goals and six assists in his last three games against Washington, but James Neal has three goals and three assists in his past three matchups.