Last years Melbourne Cup winner Prince Of Penzance is unlikely to race again after the seven-year-old fractured his off-fore leg when finishing fourth in the Herbert Power Stakes.
Prince Of Penzance will undergo surgery at the Ballarat Veterinary Practice on Monday.
“I would suggest that the overwhelming likelihood is that he’ll be retired,” said McGregor.
“The soundness and happiness of the horse is paramount to us.
“By the time he recovers and is fit again he’s going to be eight-years-old so I highly doubt that he’ll race again.”
Prince Of Penzance shot himself and jockey Michelle Payne into stardom last year when the pair won the Melbourne Cup at triple figure odds.
Before coming out of the market Prince Of Penzance was a $34 shot in the Melbourne Cup 2016.