BOSTON — Auston Matthews is unlikely to be available to the Toronto Maple Leafs on Tuesday night, according to a person briefed on the matter.

Matthews has been battling an illness and was forced to sit out the third period of Saturday’s Game 4 against the Boston Bruins. According to sources, he is also believed to be nursing an undisclosed injury, which made it more likely than not that he wouldn’t be able to play Tuesday with the Leafs trailing 3-1 in the best-of-seven series.

He appears to be doing everything he can to try and play.

Matthews was the first Leaf to hit the TD Garden ice for an optional morning skate on Tuesday – appearing at 11:08 a.m. for the scheduled 11:30 a.m. skate. It looked like a sign that maybe he would be available to play in Game 5.

Matthews worked directly with Leafs assistant coach Manny Malhotra.

The two fired pucks back and forth to one another from a close distance. Matthews received passes on his forehand, brought the puck quickly to his backhand, and then flung it back to Malholtra. Then, Matthews stood in front of the net and tipped pucks that Malhotra shot from distance. He got his stick on just about every one of the dozen or so Malhotra fired.

And that was it.

Matthews didn’t exert himself much at all, which is noteworthy because, as head coach Sheldon Keefe explained over the weekend: “The effects have lingered and gotten worse when he’s on the ice asserting himself.”

Matthews left the ice after just eight minutes. He sat out practice entirely on Monday.

Though the Leafs didn’t officially rule him out for the game, Keefe didn’t seem overly optimistic about the possibility of Matthews playing when speaking with reporters. Should Matthews be unable to go, it would be only the second game he’s missed all season after sitting out one in December due to illness.

It would also be the first playoff game he’s missed during an eight-year NHL career.

“It’s always the doctor’s call,” Keefe said. “The doctors always make the call for the players in their best interests. They don’t put anybody in harm’s way.”

Team doctors pulled Matthews from Game 4 after the second period.

Matthews has three points in the series – a goal and two assists all registered during Toronto’s Game 2 victory at TD Garden that saw Matthews score the game-winner in the third period.

At Monday’s practice, Max Domi replaced Matthews on the first line with Tyler Bertuzzi and Mitch Marner and also skated in his spot on the team’s top power-play unit.