The frontman injured his limb in June (15) when he fell off a stage during a show in Sweden and he cancelled concerts and underwent surgery.

Grohl told the crowd at Fenway Park that orthopaedic surgeon Dr. Lew C. Schon helped fix his leg, and he then invited the medic onstage to share vocals on a cover of The White Stripes' hit Seven Nation Army.

After the song, Schon left the stage and Grohl said, "Holy s**t, that's actually my doctor... What a bada*s."