You can see in the video above when the injury occurred, coming when he was checked into the boards. What's not evident is what the injury could be, perhaps his shoulder but it's anybody's guess.
The Blackhawks are in no danger of missing out on the playoffs but they're in a fight with the Blues and Avalanche for home-ice advantage when the playoffs come around. Certainly not having one of their best forwards -- and that's saying something -- will be tough.
Hossa is great at both ends of the ice, ranking fourth on the team with 50 points (24 goals, 26 assists) and is underrated for his defensive prowess too, perhaps because he's a winger.
In the next two weeks the Blackhawks will play bhe Avalanche twice -- starting Tuesday -- and if Hossa is out for three weeks then he could miss a game against the Blues as well on March 19. With suck key points up for grabs, they'll hope he can get back on the ice quickly.