Martinek remained on the ice after he was checked into the boards behind the Islanders' net by Canadiens left wing Guillaume Latendresse.
Play suddenly stopped seconds later at 12:16 and members of the Islanders' training staff hurried to Martinek, who didn't get up after he landed awkwardly on his left ankle when he bounced off the boards after absorbing the seemingly harmless check.
Martinek, who assisted on Miroslav Satan's opening goal 1:44 into the game, was sitting up as he was taken off the ice on a stretcher and to a nearby hospital for X-rays.
"There's a little fracture, I believe," Islanders coach Ted Nolan said. "He'll probably be out for four to six weeks. We don't know the length of the injury yet, but it doesn't look good. Hopefully he'll be back in six weeks."