Heavy rain in Adelaide has forced a change of tracks and lowered trainer Leon Macdonald's expectations ahead of the return of Australian Derby aspirant Gamblin' Guru.

Saturday's meeting will be run on the inside Parks track at Morphettville with Gamblin' Guru now running over 1000 metres instead of 1100.

The gelding has not been seen since his determined win on heavy ground in the Geelong Classic (2200m) in October.

"The change of tracks and the shorter distance will diminish his chances," Macdonald said.

"I thought he would be hard to beat on the bigger track but over 1000 metres on the smaller one, I don't know.

"I know he can handle the wet and I have to run him but it's changed things a bit."

Gamblin' Guru is by English Derby winner New Approach out of Glory Guru, a half sister to Gold Guru, who Macdonald and owner Harry Perks brought to Sydney in 1998 to win the Australian Derby.

The two made the decision after the Geelong win to bypass the Victoria Derby, believing Gamblin' Guru needed to mature before taking on elite company.

"He has strengthened up and we'll see what he does tomorrow before we decide his next race," Macdonald said.

"It could be a 1200 metre race at Morphettville or we could step him up to 1400 interstate. I just don't know."

With stable rider Clare Lindop nursing a shoulder injury, Jason Holder takes the ride on Saturday.