Ottawa head coach Paul MacLean officially announced the move on Monday afternoon.
Michalek was listed as day-to-day after suffering a concussion during a 3-2 overtime victory against the Buffalo Sabres on December 13. He will miss a total of five games while recovering.
At the time of the injury, Michalek was the NHL's leading goal scorer with 19. He has since been surpassed by five players, including current leader Marian Gaborik of the Rangers, who has scored 21 times.