After initially being declared questionable to return, Dalton was downgraded moments later and returned to the sideline with a black cast around his right hand.
The starting signal-caller was hurt at some point during the Bengals' opening drive, one that ended with him throwing an interception to Steelers defensive end Stephon Tuitt.
In addition, tight end Tyler Eifert was knocked out of the game during the Bengals' opening drive and was placed under concussion protocol after taking a hard hit to the head from Steelers defender Mike Mitchell. Mitchell was flagged for hitting a defenseless receiver.
Dalton was attempting to get the ball to running back Giovani Bernard on a screen, but Tuitt moved right by Bernard, guessed right and picked off the pass. Dalton immediately stepped up to tackle him. It's unclear if he was hurt on that play, but cameras appeared to show his right hand hitting Tuitt's knee on the tackle.
Just after the interception, Dalton jogged with trainers into the Bengals' locker room for evaluation; he was later declared out.
He was replaced by backup AJ McCarron, a second-year quarterback who appeared in the past two games, going 3-for-4 with 22 yards in garbage time. The former Alabama star, who announced with wife Katherine Webb last week he was expecting his first child, hadn't played extended minutes like this in the regular season throughout his career.
Dalton hasn't missed a start in his entire career. His 74.4 Total QBR entering this week was the third-highest in the league.