McQuaid was skating after a loose puck in the Boston zone when he took a hit from Washington's Zach Sill about five minutes into the second period. McQuaid was facing the boards when Sill arrived, and the hit drove McQuaid's forehead into the glass.
McQuaid stayed down for several minutes before he was helped from the ice and to the locker room.
Boston fans booed when there was no penalty on the play.
After the game, Bruins coach Claude Julien did not have an update on McQuaid. Julien believes the league should review the play and said he didn't get an explanation from the on-ice officials as to why no penalty was called.
"They didn't, I guess, seem to get a good look at it or just seemed to think it was maybe two minutes at best," Julien said. "I had the luxury of going back to my office and looking at the replay. Obviously, for me, there should have been a call there, but you know, we'll see how the league deems it. It was definitely a hit from behind in my book, but we'll let the other people take care of it, as always."
Earlier on that shift, McQuaid hit Sill in the corner, and the Washington forward went awkwardly into the boards after tripping over a couple players on the ice. As play continued in the Bruins' end, Sill hit McQuaid later in the shift.
Capitals coach Barry Trotz had no issue with either hit.
"Just hockey hits," he said. "I couldn't see the original hit [on McQuaid], but then when I saw the replay -- that's just a hockey play. Unfortunately, McQuaid got hurt there, but that's 100 percent a hockey play, and it was absolutely the right call on that, so nothing wrong with the hits."
ESPN.com's Joe McDonald and The Associated Press contributed to this report.