Toronto Maple Leafs star William Nylander's absence from the lineup is due to a migraine so severe that the club's medical staff tested him to see if he had a concussion, sources told Sportsnet's Elliotte Friedman.
Team doctors have been unable to diagnose Nylander's exact condition, Friedman adds.
The productive winger missed the first three games of the Maple Leafs' first-round playoff series against the Boston Bruins, in which Toronto trails 2-1 following a 4-2 loss in Game 3 on Wednesday night. He played all 82 regular-season games and matched his career high of 40 goals while setting new personal bests in assists (58) and points.