Former Toronto Maple Leafs assistant general manager Mark Hunter believes the Maple Leafs made a mistake not extending William Nylander, Auston Matthews and Mitch Marner all at once this past off-season.

“Oooh, big, big [challenge],” Hunter told the Toronto Star of keeping the three forwards on Monday. “It’s easy to look back, but last spring was the time.”

Matthews and Marner are currently playing out the third and final years of their entry-level contracts, while Nylander, a restricted free agent, remains away from the team while awaiting a contract.

Nylander must sign by Dec. 1 in order to play in the NHL this season and, while the Maple Leafs have been adverse to trading the 22-year-old winger, TSN Hockey Insider Darren Dreger reported Monday the team is exploring all avenues with the deadline looming.

Hunter said he believes the Maple Leafs should hold on to Nylander since they'll struggle to replace his talent.

“That’s a tough situation now. He’s a hell of a player,” Hunter said. “People say trade him. Yeah, but who are you going to replace him with? He’s a top-end player. Everybody talks about one [bad] playoff round. One playoff round is not going to define a top-end star player like him.”

Nylander scored 20 goals and posted 61 points in 82 games last season. He had one goal and four points in the team's seven-game first-round postseason series against the Boston Bruins.

Hunter left the Leafs organization in May shortly after the team promoted fellow assistant general manager Kyle Dubas to the general manager role. He is currently serving as general manager of the OHL's London Knights.