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.
You've got to focus on playing good hockey. When we do that we give ourselves a chance to win games. Win games and then maybe we''ll have a chance at the end. You can't worry about something like (the division title) when we're not playing our best hockey down the stretch. We'll figure things out together the way we always do and get back on the right page.
— Blackhawks captain Jonathan Toews after loss to Flyers on Wednesday left them five points out of first place in Central Division