Jeff Fenech has undergone lifesaving surgery in Thailand.

Already fighting pneumonia, Australia's greatest boxer was rushed to a Bangkok hospital on Monday after antibiotics failed to remedy an infected valve.

On Wednesday morning (AEST) the Hall of Fame boxer underwent successful surgery on the infected valve with doctors draining fluid that had collected in his lung. Reports say the operation was done with Fenech sitting up.

Family rushed to his side before the surgery and are now waiting for the sedated champion to wake.

Fenech had been in Thailand a number of boxers, including prodigious talent Brock Jarvis.

The former world champion had been in severe pain and was coughing up blood before being rushed to hospital.

Team Fenech trainer Basil Nassis, who originally persuaded Fenech to go to hospital after calling an ambulance, told 9News before the surgery that Fenech is preparing himself for the fight of his life.

"The fighter that he is I'm starting to see that he's preparing himself for what's ahead," said Nassis.

"Even here they're telling him it's going to be a three or four day recovery of getting up and he looked at nurse and said I'll be up in one day."

Fenech's daughter Jess is getting married on Saturday week in Sydney but her famous father has now been told he will be remaining in a Thailand hospital for at least another four weeks.

Fenech, 55, is gutted he will miss the wedding. He has been in tears.

Former heavyweight champion and Fenech's former student, Mike Tyson, called to see how his old trainer was, said close friend and businessman Mark Bouris.