The forward skated off holding his left arm to his side after hitting forward Anthony Duclair in the second period of a 5-4 overtime loss at the Florida Panthers on Thursday and did not return. The Capitals placed Mantha on injured reserve Friday.
Capitals coach Peter Laviolette said there's no timeline for how long Mantha will be out.
Washington already was without forwards
Nicklas Backstrom
, who is on long-term injured reserve and hasn't played this season because of a left hip injury, and T.J. Oshie, who is on injured reserve with a lower-body injury he sustained blocking a shot against the Detroit Red Wings on Oct. 27.
"It's a good challenge for our group," Laviolette said. "Obviously, we miss those guys. They're great players, 'Backy' being out for this long and to lose T.J. and Nic Dowd
and two draft picks to Detroit. The 27-year-old has scored 208 points (101 goals, 107 assists) in 326 NHL regular-season games with the Red Wings and Capitals. He missed 20 games during the 2019-20 season with a right-shoulder injury.
With their slew of injuries, the Capitals have had to rely on their young depth, which includes Lapierre;
Aliaksei Protas
, who made his NHL debut at the Tampa Bay Lightning on Monday before being reassigned to Hershey on Thursday; and rookie forwards Connor McMichael and Brett Leason.
McMichael scored his first NHL goal Thursday to help the Capitals rally from down 4-1 after Leason scored his first NHL goal against the Lightning on Monday. Rookie defenseman Martin Fehervary and Lapierre also have scored their first NHL goals this season.
"When guys go out, other people have to step up," Laviolette said. "I thought that everybody played well. Really good game (Thursday) to fight back into that game, we get contributions. I thought [McMichael] stepped up his game, Leason was good, Marty Fehervary's been good. 'Lappy' will get a chance to go back in there tomorrow and contribute and help. We need these guys. Right now we need them, and they've done a good job."
The Capitals recalled Protas from Hershey on Friday but sent him back down Saturday.
