Melbourne Cup winner Subzero has fought off a bout of colic but remains seriously ill.

The 1992 Cup winner has been transferred to the Bendigo Equine Hospital as vets deal with a kidney problem.

Subzero was trained by Lee Freedman but has been in the care of Graham Salisbury since his racing retirement, firstly a clerk of the course mount and in his later years for racing promotions.

Salisbury said Subzero fell ill with colic on Sunday and had recovered but now his kidneys are a major concern.

"He's over the colic alright but his kidneys are not real flash," Salisbury told RSN927.

"I've got to take him in and keep him on a drip to keep his kidneys flushed."

Salisbury, who is battling cancer, said Subzero underwent the same problem around three years ago.

Subzero turns 31 next week and Salisbury said it could take seven to 10 days to recover from the kidney complaint.

He said Subzero was off his feed and in some pain.

"He's a strong old horse and he's got a great will to win all the time," Salisbury said.

"He beat the colic, now he's got to beat the kidney problem like he has before.

"Fingers crossed he can do it again."

Mighty Boss, the 2017 Caulfield Guineas for trainer Mick Price, has died from a colic attack.

"Terribly sad for (owner) Mr Yaseen and everyone at the stable to lose Mighty Boss to colic," Price tweeted.

"A magnificent colt with most unique personality - he will be sorely missed."