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.
He's, believe it or not, actually one of my favorite guys, and I've ended up trading him twice. I appreciate what he's done. He was one year away from being an unrestricted free agent, and I felt with this opportunity, that it was a chance that we were able to get somebody for him in Nick Bonino and Adam Clendening.
— Penguins GM Jim Rutherford on forward Brandon Sutter