The 69-year-old musician, a long-time member of Bruce Springsteen's band, is seriously ill after going through a series of medical issues over the past few months, reports Rolling Stone.
The performer recently contributed saxophone to Lady GaGa's new album Born This Way and can be heard performing solos on album track 'Hair', as well as the popstar's new single 'The Edge Of Glory'.
Clemons also joined GaGa on stage for a live rendition of 'The Edge Of Glory' on the American Idol finale just a few weeks ago.
There have been no confirmed reports of the severity of the stroke, with Clemons's people yet to release a statement on his condition.
Watch Clarence Clemons perform with Lady GaGa on American Idol below: