Bee Gees co-founder Robin Gibb
is undergoing tests in a U.K. hospital for abdominal pain and inflammation of the colon. He was rushed there by ambulance on Thursday after complaining of pain.
Gibb's wife of 25 years, Dwina, is by his side at Radcliffe Hospital in Oxford, England, and is "desperately worried" about his health, the singer's rep tells PEOPLE.
There is also a Gibb family history of gastrointestinal problems. In 2003, Robin's twin brother Maurice died
after suffering intestinal complications.
Gibb had been due to perform in the BBC's religious TV concert Songs of Praise
, but had to pull out because of his illness.