The 71-year-old singer is being treated in a Tokyo hospital for a viral infection, it was confirmed on Thursday. His spokesman has said the Beatles star is expected to make a full recovery.
Paul McCartney has had to cancel several concerts due to being ill
Sir Paul had to cancel a string of tour dates when doctors said he was not fit enough to perform.
A statement released on his behalf said his treatment had been successful and that doctors had "ordered (him) to take a few days rest".
It added: "Paul has been extremely moved by all the messages and well wishes he has received from fans all over the world."
Paul McCartney has thanked his fans for all their well wishes and support
The music icon is in Asia as part of his world tour, and was next scheduled to perform in Seoul next Wednesday. But his illness has forced him to cancel that concert, along with four other gigs in Japan.
Sources close to Paul said he is very upset about the cancellations. A message on his website said, "He has been doing all he can to get better. He has only ever had to reschedule a handful of shows in his entire career. He hates to let people down."