The forward sprained his MCL in the second period of a 3-2 overtime loss to the Vancouver Canucks on Sunday in a knee-on-knee hit by Canucks defenseman Alexander Edler.
Edler, who received a major penalty for kneeing and a game misconduct, was suspended for two games by the NHL Department of Player Safety on Monday.
"Massive. He does a lot for us," Toronto forward Mitchell Marner said of Hyman. "He can play really anywhere in the lineup. Power play, penalty kill, 6-on-5, 5-on-6. So he's a big part of our team."
Hyman has scored 33 points (15 goals, 18 assists) in 43 games this season. He is second on the Maple Leafs in goals behind Auston Matthews (33) and fourth in points.
"I think, all things considered, if he can get himself back in two weeks, that would be great news for us," Toronto coach Sheldon Keefe said Monday. "These types of hits and that type of contact can have some pretty bad results. So let's take it as 'Hymes' can come back strong and rested and ready to go for us, and our team will just press on.
"Of course we'll miss him, but other people will step up and that in itself will make us a stronger group here down the stretch."
The Maple Leafs (28-12-5) are first in the seven-team Scotia North Division, four points ahead of the second-place Winnipeg Jets, but they have lost four games in a row (0-2-2). The top four teams will qualify for the Stanley Cup Playoffs.
Forward William Nylander will play at Vancouver on Tuesday (9 p.m. ET; SN, ESPN+, NHL.TV) after he was late to a meeting Monday.
"It's not about punishment, it's about growth and that's how we'll approach it," Keefe said. "So he will play tonight and our team of course is better when he's in the lineup."
Nylander scored his 100th NHL goal Sunday in his return to the lineup after missing five games because of NHL COVID-19 protocol. He skated as an extra at practice Monday.
"We had discussions and circumstances have changed a little bit since, since our initial decision yesterday," Keefe said. "More importantly to that, the situation really allowed us to have some really good discussions as a team that I think will not only serve Nylander] well, but also our entire group in terms of the accountability to each other."
Toronto could have Nick Foligno in the lineup
[for its game at Winnipeg on Thursday
. The forward was traded to the Maple Leafs on April 11 in a three-team deal involving the Columbus Blue Jackets and San Jose Sharks, but was required to quarantine for at least seven days due to COVID-19 protocols after arriving in Toronto because he crossed the United States-Canada border.
Keefe said Foligno is expected to join the Maple Leafs in Winnipeg on Wednesday.
Frederik Andersen joined his teammates midway through practice Monday, but Keefe said it's too early to say when the Maple Leafs' No. 1 goalie will play. Andersen has not played since March 19 because of a lower-body injury.
"What injuries do is it creates opportunities for others, forces some changes in different things," Keefe said." So yeah, we've got other people that have played well for us, that can fill in, and we've played without important people throughout the season and played some of our best hockey when we missed guys.
"So we've just got to give 'Hymes' time to get healthy and know that he'll come back strong. But our team shouldn't miss a beat."
NHL.com staff writer Mike Zeisberger and independent correspondent Kevin Woodley contributed to this report
