Watkins took a hit from a Steelers defender on a third-down pass from EJ Manuel, which fell incomplete but was negated by a separate Steelers penalty. The rookie receiver immediately grabbed for his side, under his left arm.
Trainers and team doctors examined Watkins on the sideline before he walked to the locker room under his own power.
The Bills lost the game, 19-16.
In May, the Bills traded their 2015 first-round pick to select Watkins, the former Clemson star, fourth overall.