The incident occurred during the third period of the Blackhawks' 4-3 shootout victory over the Canucks.
Hansen appeared to hit Hossa in the back of the head with a forearm as the veteran Blackhawks forward was reaching for a puck in the air. Hossa had to be helped off the ice and didn't return to the game.
"It wasn't even a penalty," Canucks head coach Alain Vigneault said after the game. "Both referees looked at the play. Until (Blackhawks forward Jonathan) Toews went out to talk to them, it wasn't even a penalty."
"I think everybody saw it," said Blackhawks head coach Joel Quenneville. "Everybody can have their own opinion. So we'll let the people who do that stuff do their job."
This is the first NHL suspension for Hansen during his seven-year career, though he was suspended for one game at last year's World Hockey Championship for a hit from behind.
Hansen has three goals and four assists in 15 games this season.
Last year, Hossa suffered a concussion after a high hit by Phoenix Coyotes forward Raffi Torres during a first-round playoff matchup.