The U.S. leg of his "Out There" tour was expected to go ahead as scheduled starting in Lubbock, Texas, on June 14.
McCartney, 71, postponed two shows in Tokyo earlier this week due to illness and on Thursday cancelled more concerts due to take place in Japan this week and South Korea next week.
"It has been confirmed that Paul will no longer play Seoul on Wednesday 28th which would have been his first-ever concert in South Korea," a statement from his publicist said.
His publicist declined to give any further details on his illness and his manager could not be immediately reached for comment.
McCartney rarely cancels concerts and said in a statement this week that he hated to disappoint his fans. He came to Japan after a South American tour.
McCartney and drummer Ringo Starr are the two surviving members of the Beatles, which broke up in 1970.
A native of Liverpool who largely taught himself how to play, McCartney has been known for a long and versatile musical life that included a stint with the band "Wings" after the Beatles, followed by a flourishing solo career.