The frontman suffered a number of fractures when he fell from the stage during a concert in Sweden last week (ends14Jun15) and he flew to London to undergo an operation on Monday (15Jun15).
Grohl had six metal screws inserted in the leg and was advised by medics to cancel all of the band's remaining European tour dates, including their Friday headlining slot at the fabled U.K. festival.
Florence + The MAChine, who were scheduled to play the set before the Foo Fighters, have now been boosted to headliner status and the rest of the bill has been revised.
Organiser Emily Eavis says,"Once we heard the sad news that Foo Fighters had been forced to pull out, there was only one person we wanted to call and that was Florence. Every time she has played here she's done something spectacular and we always knew she would headline the Pyramid one day. I'm delighted she's agreed to step up to it - she's going to smash it!"
Following the announcement, the Foo Fighters showed their support by tweeting, "Go Florence!!!!"
The festival in Somerset, England takes place between 25 and 28 June (15).