PITTSBURGH -- The play has been debated and dissected. Now there is a diagnosis.

Pittsburgh Penguins captain and NHL star Sidney Crosby has a concussion after leaving Game 3 of an Eastern Conference semifinal against the Washington Capitals. Crosby will miss Game 4 Wednesday at PPG Paints Arena and then will be monitored per the league's concussion protocol.

There is no target date for Crosby's return, although Pittsburgh coach Mike Sullivan on Tuesday described Crosby as "very upbeat. He's very positive. We're very optimistic, and we're hopeful that we'll get him back in a timely fashion."

Monday's 3-2 overtime win got Washington back into the series, trailing 2-1.

"Right where we were last series (against Toronto)," defenseman Nate Schmidt said. "You're down 2-1 having a chance to win a Game 4 and go back home tied up, and go from there."

Whether Crosby, a finalist to win what would be his third Hart Trophy as league MVP, will suit up before the end of this round is unknown. Crosby has four goals and 11 points in eight games this postseason.

This is at least the third concussion for Crosby, who missed the first six games of the 2016-17 season because of one. Earlier, he missed half of 2010-11 and most of the following season because of concussion and neck problems.

Crosby wasn't the only Penguins player injured Monday. Winger Conor Sheary, who left after colliding with teammate Patric Hornqvist, also has a concussion.

Sheary skated separately before Pittsburgh held an optional practice Tuesday, but his timetable is as inexact as that of Crosby, who was at the team's practice facility but did not skate.

Sullivan declined to divulge lineup changes or revised matchups he might look for with those two players out.

"We have capable guys," Sullivan said. "We'll put combinations together that we feel will give us the best chance to win."

Two players who will be counted on to help fill the void are center Evgeni Malkin and winger Phil Kessel, who lead Pittsburgh -- and, going into Tuesday's games, the NHL -- with 15 and 12 points, respectively, this postseason.

"(Malkin) is an elite player. He has that ability," Sullivan said. "We're going to rely on him that much more, and we believe he'll get the job done for us. I don't think the burden falls on him solely. But (Malkin) is going to have to bring his very best game to help us win. Phil's the same way, and then it goes down the bench."

One player who will be available for Game 4 is Washington defenseman Matt Niskanen. He got a cross-checking major penalty and game misconduct for the which Crosby got hurt. Niskanen will not face supplemental discipline from the NHL.

"I thought it was the right decision," Capitals coach Barry Trotz said. "You had two forces coming across. ... That's hockey."

The play happened at 5:24 of the first period Monday. Crosby, going to the net on a two-on-one break, got thwarted by goaltender Braden Holtby. Near the crease, Crosby's left skate was clipped by the skate of Washington's Alex Ovechkin, who then appeared to slash Crosby in the back, only to have his stick bounce up and hit Crosby in the helmet.

Crosby struggled to regain his balance as he moved to his right, where he crumbled as he was met by a Niskanen cross-check to his face. While it looked as though Crosby's left leg bent awkwardly, Sullivan said the only injury is the concussion.

Even though Pittsburgh is known more for skill and speed than for tough, physical play, the Capitals are prepared to face a club fired up over losing Crosby.

"Yeah. I mean, it should be nasty. It's the playoffs," Washington center Jay Beagle said. "That's the way we like to play. That's the way they like to play. Hard hits. Going after each other. These are two teams that don't like each other.

"It's fun to play hard between the whistles. After the whistles, you never want to get a penalty. There were a couple of times the refs were warning us, both sides, and if you take a bad penalty and it's something after a whistle, that's when you've got to make sure emotions are in check."

The Penguins will be channeling some of their emotion toward playing a strong game in Crosby's absence.

"He's our leader," winger Carl Hagelin said. "We showed a lot of resilience last game. After he got hurt, we started playing with a lot of intensity, a lot of emotion. If he's not going to play next game, we'll play that one for him."