Decker, the team's leading receiver, was helped off the field and went straight to the locker room. The Denver Post reported that he suffered a sprained MCL and will not play in Saturday night's divisional game against the New England Patriots.
Decker was scheduled to undergo an MRI on Monday, the newspaper reported.
The second-year receiver hauled in a pass over the middle, but was immediately tackled by Harrison, who went low to bring Decker down on a play first ruled a catch and then overturned on replay.
Harrison has a history of hits to the head. He was suspended last month because of his helmet-to-helmet hit on Cleveland quarterback Colt McCoy, who suffered a concussion.
Already banged up on the offensive line, the Steelers had left tackle Max Starks leave with a right knee injury. They were already without All-Pro center Maurkice Pouncey, who missed the game with an ankle injury.
The Broncos won 29-23 in overtime.
Information from The Associated Press contributed to this report.