Tony Kornheiser and Michael Wilbon are skeptical that Sidney Crosby returns to play the Capitals, which could change the complexion of the series. (1:52)

Pittsburgh Penguins captain Sidney Crosby will not play in Game 4 against the Washington Capitals on Wednesday because of a concussion he suffered in the third game of the series, coach Mike Sullivan said on Tuesday.

Crosby has a concussion history and missed the first six games of this season because of a concussion. He is now in the concussion protocol, Sullivan said, and listed as day-to-day.

Crosby left Game 3 of his team's playoff series, a 3-2 overtime loss to Washington, after he took a first-period cross-check to the head from Capitals defenseman Matt Niskanen. His leg also bent awkwardly during the collision.

Penguins captain Sidney Crosby had to be helped off the ice after being cross-checked across the face during the first period Monday. Charles LeClaire-USA TODAY Sports

Crosby lay on the ice for several moments before slowly getting up and skating off, mostly on his own power. He went directly down the tunnel for treatment. Crosby did not return to the game.

"He's very upbeat and positive," Sullivan said of his star. "We're very optimistic and hopeful we'll have him back in a timely fashion."

Crosby's diagnosis wasn't the only bad news for the Penguins. Forward Conor Sheary was leveled Monday when teammate Patric Hornqvist missed a check on the Capitals' Lars Eller and hit Sheary instead. Sullivan said Tuesday that Sheary is also in the concussion protocol, thinning the Penguins even further with Pittsburgh clinging to a 2-1 series lead.

Sheary skated on his own before the Penguins' optional practice on Tuesday, but Crosby was not on the ice.

Niskanen received a major and game misconduct penalty for the hit on Crosby. An NHL source told ESPN on Tuesday that Niskanen will not have a hearing with the league regarding further discipline.

Sullivan would not give his opinion on Niskanen's hit after the game. But the Penguins' Chris Kunitz was not as reluctant to talk about it.

"I like Nisky as a person," Kunitz said. "I don't think it's a very nice hit. I don't think it's something this game is looking for, especially against someone who means so much to our team."

"We saw him laying there, and obviously it was tough to see," teammate Justin Schultz said. "He's our best player, best player in the world, and we hope he's all right."

The hit from Niskanen, a former Penguins teammate, came as Crosby was already going down after getting clipped by Alex Ovechkin while driving in on Capitals goalie Braden Holtby.

Niskanen said after the game that he wasn't trying to hit Crosby in the head, explaining that Crosby was moving "lower and lower" as the two came together in front of the Capitals' net.

"I hope he's OK. I certainly didn't mean to injure him," Niskanen said. "It was an unfortunate play."

Crosby has dealt with multiple concussions during his career, including one against Washington in the 2011 Winter Classic that he needed nearly two years to fully recover from.