A blow to the back of Hossa's head by the Vancouver Canucks' Jannik Hansen early in the third period was the cause, and Chicago now must hope Hossa doesn't have a recurrence of the concussion symptoms that stemmed from a hit by Raffi Torres that knocked him out of a Stanley Cup Playoff series against the Phoenix Coyotes last spring.
After scoring a pair of goals in the second period of a 4-3 shootout victory, Hossa was dropped to the ice 1:10 into the third when he and Hansen collided while competing for a puck in the air.
Hossa was face down on the ice for a few minutes before heading to the locker room. He didn't return to the game.
"I saw him after the game. He seemed to be doing okay, but we'll know more [Wednesday]," Blackhawks coach Joel Quenneville said.
Following the injury from the Torres hit, Hossa wasn't cleared to return to action until early December, and was off to a strong start to the season, scoring eight goals and adding six assists.
Hansen was assessed a two-minute minor for roughing on the play.
"We were both jumping for it," Hansen said. "Again, he grabs the puck first, and then as I'm coming down I land on him a little bit. Apparently I hit him in the back of the head, (that's) what the ref is telling me once I [came] down. But again, it's hard for me to tell what really happened.
"It's a hockey play and we bumped together a little hard and he goes down. I can't really do anything about that. We both go for the puck and we ran into each other. Obviously, we know he got hit last year. I think everybody in the hockey world knows that, but again, it's a hockey play and when you go for a puck, you go for a puck.
Hossa's teammates are simply hoping to have the star winger back in in the lineup as soon as possible. The Blackhawks, who joined the 2006-07 Anaheim Ducks as the only teams to record at least one point in the first 16 games of a season, host the San Jose Sharks on Friday at the United Center.
"I'd have to see the replay a few more times, but I didn't like the hit when I saw it and I like it even less when you see a guy like Hoss on the ice, who has been through something like that before," Chicago winger Patrick Sharp said. "I'm not sure how he's feeling, but hopefully he's doing okay."
Added captain Jonathan Toews: "That's ugly and very unfortunate. You never want to see that. I don't know the situation yet, but we hope that it's just a minor scare for now and that he'll be back soon. I saw it when the puck was up. I saw the replay on the board and it's pretty evident that he wasn't reaching for the puck or anything. I'm not too sure exactly what's going to happen there. I'd have to see it a few more times before I comment any further. I don't think there was any doubt that there was contact to the head there and we just hope that Hoss is going to be okay."
Hossa was named the game's No. 1 star.