John Farnham is unlikely to perform again after being admitted to hospital with a respiratory infection.
It comes just several months after John, 73, underwent a 12-hour operation to remove cancer from his mouth.
In a statement, his family confirmed that he was suffering from a lung infection but was responding well to his treatment.
His relatives said: "He is currently being treated for a respiratory infection in hospital, but he is comfortable and receiving the very best care."
In August, John was under the knife at a Melbourne hospital for 12 hours to remove a tumour in his mouth, not too long after being diagnosed with mouth cancer.
However, he was only diagnosed with the tumour after his wife made him visit the doctor for a check-up.
Following the surgery, a spokesperson for the I Can't Dance to Your Music singer said he was "unlikely" to ever perform again.
Speaking about his admission, his wife of 50 years, Jill, said: "John continues his recovery following last year's successful surgery.
"He's always been a strong and determined person with everything he's ever done and we are all so proud of him, he is responding well to the specialist care he's receiving."
She went on to thank the staff who have been looking after him for the past six months, as well as his legion of fans for their continued support, saying: "The family would like to re-iterate their appreciation for all the medical staff that have attended to John over the past six months and for all the kind messages that been received from across Australia and the world."
The hitmaker was admitted to intensive care for over a week after his surgery, which saw him have part of his jaw removed before undergoing reconstructive surgery.
Ahead of his operation, John said that his cancer diagnosis was something that people faced on a regular basis, adding: "and countless others have walked this path before me."
Glenn Wheatley's widow, Gaynor, said his family only discovered his diagnosis a mere few weeks prior to his operation, telling The Today Show: "I think John suffers from that man thing that says 'I'm fine', and was lucky, and we have Jill to thank to take him to the doctors (where they) found this legion in his mouth which has now been taken out and addressed."
Gaynor later claimed that there were 26 surgeons in the operating theatre for the operation.
