PITTSBURGH — One guy in, another out, and so it goes as the flu runs around another NHL locker room.

The Rangers got forward Jesper Fast back for Thursday night’s 4-1 loss to the Penguins at CONSOL Energy Center after he missed Monday’s 2-1 win over the Blue Jackets at the Garden with the illness. However, defenseman Marc Staal was forced to miss the game against the Penguins, left back at the hotel and not feeling well.

The Rangers’ first reported case of the flu this season was Dan Boyle just before the Feb. 17 game against the Blackhawks. Rookie winger Marek Hrivik then was feeling bad during the team’s two-game trip last week through St. Louis and Dallas. Neither missed a game.

Yet when it comes to containing it, that’s a hard task — one training staffs always are strapped with this time of year.

“Our medical staff is on top of that. They’re doing what they can,” said coach Alain Vigneault, a little froggy in the voice himself. “If it happens, it happens, but hopefully we have it contained at this time.”

In Marc Staal’s absence, veteran defenseman Dan Boyle switched to the left side, paired with rookie Dylan McIlrath. McIlrath had played forward on Monday, getting only 4:54 and no shifts in the third period.

The assimilation of Eric Staal into the forward group is still developing, as Vigneault started him again at center, between Viktor Stalberg and Kevin Hayes. By the third period, he moved Oscar Lindberg off the fourth line to be on Staal’s left.