Bell was catching a pass from quarterback Ben Roethlisberger early in the second quarter when linebacker Vontaze Burfict made the tackle, then appeared to celebrate with teammates from clear across the field.
Bell left Heinz Field for further evaluation and did not return. He later took to Twitter to thank fans for the outpouring of support.
I appreciate the concern and support from everybody who's sent me txts, tweets, phone calls, etc...I'll be okayy, love youu all! #Juice— Le'Veon Bell (@L_Bell26) November 2, 2015
Mike Tomlin did not update the status of Bell's injury in his postgame news conference, but Steelers players noticed Burfict's celebration.
"He's that type of guy," Steelers guard Ramon Foster said of Burfict. "That type of guy will get his sooner or later. ... If you've played against him, you know what I mean by it. He'll play it off, act dumb about it, but you don't run across the field acting hyped, celebrating, jumping up and down when a guy goes down like that."
Burfict said after the game that he immediately didn't know Bell was injured and that he was friends with the Steelers' running back.
Bell, who entered the game with 511 rushing yards in five games, was down for a few minutes and was helped off the field by trainers. But he appeared to move the knee while sitting on the cart, which could be a good sign.
Defensive end Cam Heyward said he's going to "pray for my guy Le'Veon. ... It's an unfortunate situation."
Bell, who was suspended two games earlier this season for marijuana use, and Roethlisberger, who missed four games with a knee injury, have played a total of just 39 snaps together this season, according to ESPN Stats & Information.
ESPN Staff Writer Coley Harvey contributed to this report.