Sources told ESPN that Roethlisberger suffered a sprained shoulder.
Roethlisberger was taken to a Pittsburgh hospital to undergo further tests to determine the severity of the injury to his throwing shoulder, with a diagnosis expected sometime Tuesday, sources told ESPN.
Roethlisberger was sacked by Justin Houston to end Pittsburgh's first possession of the second half. The quarterback was taken to the locker room after walking off the field, and backup Byron Leftwich began warming up. Roethlisberger finished 9-of-18 for 84 yards and a touchdown for the Steelers, who won their fourth straight game to improve to 6-3.
Coach Mike Tomlin wouldn't speculate on the severity of Roethlisberger's injury, and his status for Sunday's showdown with AFC North leader Baltimore is uncertain.
"It didn't seem like a tough hit ... but he came to the sideline and next thing you know he was gone," Pittsburgh left tackle Max Starks said. "I'm hoping it was nothing serious. Honestly it didn't seem like it."
Roethlisberger has been largely injury-free this season in offensive coordinator Todd Haley's system, which requires him to get rid of the ball quickly. Kansas City's secondary, however, shut down Pittsburgh's receivers, and Roethlisberger took a series of hits on a wet night at Heinz Field.
Leftwich replaced Roethlisberger and finished 7-of-14 for 73 yards in the victory.
Leftwich managed to lead the Steelers on one scoring drive early in the fourth that gave them a 13-10 lead.
"After four or five plays, it was like riding a bike," Leftwich said. "I took a few hits. I hadn't hit the ground in awhile. It was a whole lot of things I hadn't done in awhile. It was good."
Information from ESPN's Adam Schefter and Ed Werder, and The Associated Press was used in this report.