Mullen out for the season

MRI scans have revealed what Adelaide United had feared with defender Daniel Mullen set to miss the season after seriously injuring his knee in the 2-1 loss to Melbourne Heart on Friday night.

MRI scans have revealed what Adelaide United had feared with defender Daniel Mullen set to miss the season after seriously injuring his knee in the 2-1 loss to Melbourne Heart on Friday night.

Mullen damaged the lateral side of his right knee in what appeared to be a rather innocuous incident with the defender running through the Heart penalty area to challenge a Reds corner.

The Olyroo had earned his first start in nine games after a serious ankle injury and was covering the loss of the injured Robbie Cornthwaite in the centre of defence.

Club doctor James Ilic confirmed United's worst fears on Saturday and said Mullen will undergo surgery on Tuesday.

"Daniel had an MRI scan of his knee this morning, which indicated he has damaged the lining of the outside of the joint and sheared off some of that lining. He will have an operation on Tuesday and the surgeon will attempt to repair that, but he is unlikely to play again this season," he said.

Ilic admitted that while it seemed innocuous, Mullen is facing up to three months on the sidelines and is unlikely to play again this season.

"It is certainly an injury that can happen and while it seemed innocuous at the time, his foot got stuck in the turf and his knee twisted and presumably it happened at that time," Dr Ilic said.

"Anything is possible but it is very unlikely (he will play again this season). I think we-re probably looking at three months before he is back playing, but he will be reviewed once he has had the surgery."

Reds coach Rini Coolen admitted it is both disappointing for Mullen personally as well as United.

"He is out for the rest of the season so that is really disappointing for us and especially for him," Coolen said.

Midfielder Adam Hughes was impressive when shifted into the heart of defence to cover for Mullen and will be an option for United's game against Perth Glory on Wednesday, while Cornthwaite could also be a chance to come back into the line up after his hamstring injury.