"The surgery was exploratory and they liked what they looked at," Tomlin said. "We'll give him a couple of weeks and see how his body responds to it."
Stapleton, a third-year player from Rutgers who started the final 12 games of the regular season and all three playoff games for the Steelers in 2008, had swelling in the knee earlier this week.
He has not practiced with the team at training camp at Saint Vincent College since Sunday.
With Stapleton out and starting center Justin Hartwig limited by a toe injury, the Steelers brought in two centers for workouts Friday. But both centers, Alex Stepanovich, a six-year veteran who played for the Atlanta Falcons last season, and rookie Alex Derenthal left without contracts.
Also, safety Troy Polamalu, who had been out since Monday with a sore hamstring, returned to practice. Linebacker LaMarr Woodley sat out his second consecutive day of practice with swelling in his right knee.