Downie took a shot to the right foot during the second period of the Lightnings' 8-1 loss to the Boston Bruins on Thursday night.
Tampa Bay coach Guy Boucher was quoted in The Tampa Tribune on Friday as saying Downie could be out, "Oh, three, four [weeks], even more. Those [injuries], by my experience, take a long time."
Downie (15 points in 23 games) was on the right wing of one of the NHL's most potent lines, playing with center Steven Stamkos and Martin St. Louis. With Downie out, Boucher has for now put Gagne on the top line with Stamkos and St. Louis.