Luckless Australian UFC champion Robert Whittaker is shattered after being forced to abandon his middleweight title defence due to a “freak” abdominal injury which could have proved fatal in a bout.

Sunday’s scheduled clash with American Kelvin Gastelum at a sold-out Rod Laver Arena in Melbourne was called off in the early hours after Whittaker experienced issues on Saturday evening and subsequently underwent surgery.

‘“His bowel and his intestines poked through a hole,’” UFC boss Dana White told AAP.

“They think he’s had this problem and it’s been going in and out. It’s one of those situations, had it popped up during the fight it could have been fatal for him so this is really serious.

“Hopefully they popped it back in and sewed it up and if that’s the case, he’ll be four weeks (out of action) but this was a freak, freak injury less than one per cent.

“Our doctor here at the UFC, who has been doing this for 30 years, has never seen it ever in his career and not in a young person. It’s usually in much older people.”

It continued a terrible run of bad luck and health issues for 28-year-old Whittaker since he won the interim title in 2017.

Illness and injury forced him out of a title defence in Perth 12 months ago and he suffered a broken hand in his last bout with Yoel Romero in June 2018.

Whittaker’s manager Titus Day said the champion first reported some issues around 6pm on Saturday.

“Rob said he was a bit bloated and a little bit tired which is not uncommon when your are going through the process they are going through, reloading and putting some food back in your body,” Day told AAP.

“Then about 10 o’clock we got a call from (Whittaker’s wife) Sofia saying he’s got some bad stomach cramps and he’s in quite a lot of pain and can’t sleep and can’t go to the bathroom.

“We said we’ll call the UFC doctors and shortly after that he started vomiting so everyone was alerted and was at his room and it was monitored from there until it got to the stage at about three in the morning where he was taken to hospital.

“Rob is absolutely shattered for everyone else.

‘When I walked in, the first thing he said to me was ‘Man, I’m so sorry.’

“I was like ‘what are you talking about?’ “He’s like ‘I’m so sorry for this I’ve let people down.’

“Thats just Rob thinking of everyone else not himself.

“This was really his moment, the media and the hype that was building around him was taking him to a whole other level and I think he would have done very well in this fight.

“This is Rob’s huge moment, a special moment in his life, it’s just been shattered, so there will be a lot of pieces to be picked up, and we’ll do it.”