Michalek has played in two games since Feb. 12. He tried to return and play through the injury, recording assists against the Toronto Maple Leafs on March 6 and the New York Rangers on March 8, but hasn't been in the lineup since.
In 15 games this season, Michalek has two goals and 10 points. He led the Senators with 35 goals last season and was third with 60 points.
The Senators' top-two scorers from last season, forward Jason Spezza and defenseman Erik Karlsson, also have been out of the lineup with long-term injuries.
Just the feel for the direction they were headed and what they're trying to do, it just felt that this is a really good thing for this organization. They've got the pieces. We can put something together and go on a run or two and be together for a while, and I'm really excited about that opportunity. The team we have here has an opportunity to win, and that's the most attractive thing.
— Washington defenseman Matt Niskanen on why he decided to sign with the Capitals