Red Hot Chili Peppers frontman Anthony Kiedis is in hospital after being whisked away in an ambulance before a show in Irvine, California.
The band were meant to be headlining at KROQ's annual Weenie Roast.
Bassist Flea made the announcement that they wouldn't be performing from the stage at Irvine Meadows Amphitheatre and apologised, according to Billboard.
He told the crowd of 16,000 the band were "devastated."
Billboard reports Kiedis, 53, was taken from the venue in an ambulance suffering from "extreme stomach pain".
Weezer ended up closing the show.
Red Hot Chili Peppers were due to take the stage at just after 10 pm on May 14 (local time), however at 10:30pm, KROQ tweeted that "due to illness, the Chili Peppers were forced to cancel their set".
The festival line-up also included Panic! at the Disco, Empire of the Sun, Garbage, Lumineers, Fitz and the Tantrums and Miike Snow.
Blink-182 also performed a surprise set.
Chili Peppers drummer Chad Smith tweeted how disappointed the band was they couldn't perform and wished Kiedis well.
Their next scheduled concert is May 17 in Burbank, California.
Newshub.