The 'How Deep is your Love' hitmaker has been treated for an inflamed colon after being rushed to hospital on Thursday (13.10.11) complaining of "severe" abdominal pains.
Robin's wife of 25 years, Dwina, is by his side at Radcliffe Hospital in Oxford, England, and is "desperately worried" about his health, according to People.com.
Last year Robin - who is teetotal and a vegetarian - underwent surgery for a blocked intestine, the same condition which led to the death of his twin brother Maurice in 2003.
His manager Eaton told The People newspaper: "Obviously it is a worry. This is what did it for his brother Maurice - but what is different is his condition was left for a long time and Robin's has not been.
"Our concern is that it keeps recurring but he is determined to get better and we just hope things will be OK. Robin just wants to get back to work."
A further statement said: "Robin requests that, since this is a difficult time for him and his family, his privacy be respected.
"He would like to thank all his friends and fans for their good wishes and sends them his love."
The 61-year-old singer had to cancel a radio interview on Friday (14.10.11) because of his hospitalisation.
Robin has suffered from crippling stomach pains for years and medical professionals have been unable to diagnose an exact cause for the ailment.
Robin also has an elder sibling Barry, 65, who was the third member of The Bee Gees.