Forward Adam Cracknell also was recalled from Peoria of the American Hockey League.
Allen has been recalled under emergency conditions due to goaltender Jaroslav Halak’s lower body injury, which he suffered during the first period in the Blues' 4-1 win against the Minnesota Wild on Monday night.
Hillen, 26, has registered one assist and 10 penalty minutes in 10 games with the Capitals this season. Hillen ranks eighth on Washington in average ice time per game (18:21) after missing 25 games with an injury.
The New York Islanders will find themselves in eighth place in the Eastern Conference at the end of Tuesday night with either a victory or a post-regulation loss to the Winnipeg Jets at Nassau Coliseum.
The Islanders begin play Tuesday in ninth, but have 37 points, tied with the eighth-place New York Rangers, who aren't in action again until Wednesday.
The Jets hold down the third seed by virtue of leading the Southeast Division, but they've lost three straight and are four points ahead of the Carolina Hurricanes and Washington Capitals, who face each other Tuesday.
Here's how the lineups could look for the Islanders and Jets:
Vanek skated with the team Tuesday morning, but said he has not recovered fully from the upper-body injury that has sidelined him since March 26.
Vanek leads the Sabres with 16 goals and 33 points this season.
Mitchell had surgery on his knee in the offseason and reinjured it during the lockout. He had been trying to rehabilitate his leg during the season, but ESPN's report states that Mitchell had arthroscopic surgery on the injured knee and will miss the remainder of the season.
The veteran blueliner had career-bests of five goals and 24 points in 76 games last season, and was a plus-7 in helping the Kings win the first Stanley Cup in franchise history.
Toronto Maple Leafs general manager Dave Nonis spoke with the agent for Calgary Flames goaltender Miikka Kiprusoff on Monday and likely will speak directly to Kiprusoff on Tuesday, according to TSN's Darren Dreger.
This comes on the heels of multiple outlets reporting Monday that the Maple Leafs were granted permission by the Flames to speak to Kiprusoff, who is likely to be dealt before the NHL Trade Deadline passes Wednesday.
In four games this season, Greiss is 1-3-0 with a 2.78 goals-against average and .906 save percentage.
In two games with San Jose this season, Stalock has posted an 0-0-1 record with a 2.86 GAA and a .846 save percentage. In 31 games with Worcester, he has posted a 15-12-3 record with a 2.48 GAA and a .917 save percentage.
Tennyson, a 22-year-old undrafted free agent and California native, will be paired on defense with veteran Brad Stuart.
Here's how the lineups project for the Sharks and Canucks:
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Very happy that old guy finally scored. It was great. You see the excitement on his face. I remember when I scored my first goal and it's just such a great feeling. Anytime you can help contribute to a team win it's a lot of fun.