Now, it's uncertain when the left wing will be able to resume helping that playoff push.
Lupul will be unavailable Saturday night against the slumping New Jersey Devils as Toronto goes on the road trying to bounce back from its first regulation loss in nine games.
After going 13-11-1 with Lupul sidelined by a broken forearm, the Maple Leafs are 5-1-3 since his return -- he missed two of those games due to suspension -- to move into sixth place in the Eastern Conference. They haven't made a playoff appearance since 2004.
Lupul recorded his 14th point since returning with a first-period assist in Thursday's 5-3 loss to Philadelphia, but he left later in the period after possibly taking a hit to the head when he got sandwiched by Jay Rosehill and Adam Hall. Lupul did not practice Friday, and various reports have said he will not take the ice for this game.
"He's done a lot for us. He's a great player. I don't know how long he's out for but hopefully it's short," goaltender James Reimer said after the end of the Maple Leafs' season-best 5-0-3 run. "But if it's a couple games or a couple weeks, we've got to step up in here."
With Toronto (20-13-4) not picking up a veteran goaltender before Wednesday's trade deadline, the pressure in net falls on Reimer and backup Ben Scrivens.
Reimer tied a season high for goals allowed Thursday after going 3-0-1 with a 1.72 goals-against average in his previous four starts. He turned aside 28 shots in a 4-2 home victory over New Jersey on March 4 in the teams' only meeting this season.
Scrivens has yet to face the Devils.
There's a chance defenseman Ryan O'Byrne, acquired from Colorado on Wednesday, will be in front of one of them after not playing Thursday.
New Jersey (15-13-9), meanwhile, is trying to crack the top eight in the East after falling to ninth with Thursday's 1-0 defeat at Boston. It was the fifth straight loss for the defending conference champion.
"I'd be lying if I said we don't know where we are in the playoffs. But we're not thinking about it (every) game," defenseman Andy Greene said. "If we play 11 more games like this, I think we'll give ourselves the best chance to continue to play."
The Devils, who fired a season-high 40 shots Thursday, would boost their chances by improving their conference-worst 2.35 goal-scoring average.
Veteran forward Steve Sullivan might be able to help after being acquired from Phoenix on Wednesday for a seventh-round pick. Sullivan, who has five goals and 12 points in 33 games this season, could make his Devils debut after passing his physical Thursday.
The Maple Leafs have been getting plenty of offense from center Nazem Kadri, tied with Lupul with a team-best 14 points since March 16.
Kadri had a goal and set up another against the Devils last month. He also keyed Toronto's win in its most recent visit to New Jersey, scoring in the second period and the shootout of a 4-3 victory March 23 last year.
Devils goaltender Martin Brodeur could get his first look at the Leafs this season after missing the March 4 contest with a back injury. If he's in net, Brodeur will try to avoid losing six consecutive starts for the first time since Dec. 17-29, 2010.
Toronto has won two straight and three of four in New Jersey.