LONDON (Reuters) – British pop star Tom Jones is postponing the start of his U.S. tour, which was scheduled to begin on Wednesday, due to advice from doctors, the star posted on Twitter.

The 77-year-old Welsh singer, famous for hits including “It’s Not Unusual” and “Sex Bomb”, was due to begin his American tour on Sep. 6 in Bethlehem, Pennsylvania.

“Following medical advice, Sir Tom Jones has announced that he will unfortunately be postponing his US tour,” read a statement posted on his Twitter feed late on Friday, without giving further details about the health issue.

“Dates are being re-scheduled for May and June 2018,” it added, saying the singer “sends his sincere apologies to fans.”