The Mandy singer's representative reveals he went under the knife for an undisclosed operation on Monday, but suffered a setback in his recovery on Wednesday (10Feb16) and had to fly to Los Angeles for further treatment after completing a performance in Memphis, Tennessee.
As a result, Manilow had to postpone shows in Kentucky on Thursday (11Feb16) and Nashville, Tennessee on Friday (12Feb16) to give himself time to recuperate.
A statement posted on his Facebook page also called into question his attendance at Monday's (15Feb16) Grammy Awards, where his latest album, My Dream Duets, is up for Best Traditional Pop Vocal Album.
However, his spokesperson insists the 72-year-old is doing well and he is obeying doctors' orders for complete voice rest.
"His doctors report that the surgery was successful and they expect no further complications," the publicist said on Friday (12Feb16). "For the next 48 hours, Manilow has been instructed not to talk, sing or rap.
"Barry thanks everyone for their well wishes and concern."
It still isn't clear if Manilow will attend the Grammy Awards on Monday.
The singer has been blighted by health concerns and rumours recently - his publicist recently had to deny reports suggesting he had been hospitalised after suffering a heart attack.
Sources told news outlets the star was fighting for his life after being airlifted to Los Angeles' Cedars Sinai Medical Center on 16 January (16).
"Mr. Manilow was not airlifted to Cedars with a heart attack," the rep told Access Hollywood, adding stories linking his latest alleged health issues to heart palpitations which led to emergency care in October (15) are false.
"It is indeed an established fact that Mr. Manilow does have atrial fibrillation, but he has never had a heart attack nor is this a concern," the rep added.