Bruins coach Bruce Cassidy did not have an update on Chara's status Tuesday and said he would have to wait for the team to return home to Boston to find out more.
The best-of-7 series is tied with Game 5 at TD Garden on Thursday (8 p.m. ET; NBC, CBC, SN, TVAS).
Chara left at 3:07 after Blues forward Brayden Schenn's shot went off Chara's stick and hit him in the mouth, leaving him bloodied. Although he returned to the bench at the start the third period wearing a full, clear face shield, Chara did not take a shift.
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"He was advised not to return to play. (He) had some stitches, probably [will have] some dental work in the near future," Cassidy said postgame. "I don't know his status for Game 5. Obviously, when he gets back home he'll have to be re-evaluated, see how he feels tomorrow for starters. If we have something for you, we'll give it to you. So I can't say whether he'll play in Game 5 or not."
With Chara out, Boston relied on its remaining five defensemen. Charlie McAvoy led the Bruins with 25:51 of ice time and Torey Krug was second at 24:11.
But with Boston shorthanded, Blues forward Ryan O'Reilly scored his second goal of the game at 10:38 of the third period on a rebound in front to give St. Louis a 3-2 lead.
"I think we are wearing them down when they don't have six [defensemen]," Blues forward Oskar Sundqvist said. "Obviously, you don't want to see a guy take puck in the mouth. It's kind of like when you saw [Blues defenseman Vince Dunn] do it. But, five D against our forecheck, I don't think it's that easy."