William Nylander sits out as Toronto Maple Leafs lose Game 1

Trent Frederic seals game with empty-net score for Bruins (0:46)

Trent Frederic pads the Bruins' lead with an empty-net goal to ice the game against the Maple Leafs. (0:46)

BOSTON -- Toronto Maple Leafs forward William Nylander sat out his club's 5-1 loss to the Boston Bruins in Game 1 of this Eastern Conference first-round playoff series Saturday due to an undisclosed injury.

Nylander, who hasn't skated with the team since Thursday, did not take the ice for warmups at TD Garden, ending speculation about his availability for at least one game. Toronto coach Sheldon Keefe has not revealed any details about Nylander's ailment, which reportedly flared up after the Maple Leafs' regular-season finale Wednesday against the Tampa Bay Lightning.

Keefe did not have an update on Nylander after Saturday's loss.

Nylander is coming off a career-best 98-point campaign and is a staple among Toronto's top six forwards. He also is on the Maple Leafs' No. 1 power-play unit.

While Keefe did not confirm Nylander's status earlier in the day, his teammates appeared resigned to playing without him.

"[It's] tough for him, but hopefully he won't miss too much and he'll be back," Toronto defenseman Timothy Liljegren said. "[It's] hard to replace Willy. But we've had guys step up when guys go down all year, so it will be no different this time."

Nylander was the only Maple Leafs player to dress in all 82 regular-season games, and he hadn't missed a contest in three years.

He was missed on Saturday. Toronto amassed 36 shots on net but couldn't solve Boston goaltender Jeremy Swayman in the opener. David Kampf, with the Maple Leafs already down 4-0 in the third period, accounted for Toronto's only goal, with assists from Connor Dewar and Ryan Reaves.

Maple Leafs stars Auston Matthews and Mitch Marner combined for seven shots and nearly 41 minutes of ice time but couldn't keep Toronto from a 1-0 series deficit.

With Nylander unavailable, Nicholas Robertson stepped into the lineup, entering Toronto's third line. He finished with 14 shifts and 10:38 of ice time.

Game 2 is Monday in Boston.