A statement issued Tuesday by the musician's publicist said John was suffering from an inflamed appendix and surrounding abscess.
He has been advised by doctors to cancel his concerts while he undergoes a regime of antibiotics to treat the abscess. That will be followed by surgery in the next few weeks.
The statement said John fell ill during his recent European tour, but "is eager to be back on top form and return to play the remaining shows starting in early September 2013."
The 66-year-old performer had been due to play an outdoor concert in London's Hyde Park on Friday on a bill with Elvis Costello and Ray Davies.
Concert organizers said the show will go on - for free - with the remaining lineup and that ticket holders will receive a full refund.
Last year John canceled several U.S. dates after being diagnosed with a respiratory infection.
His new album, "The Diving Board," is due out in September.