The best insight into the chances of Brisbane sprinter Gojo Mimo winning at Randwick might be found in a prediction made by one of Australia's most successful modern-day jockeys.

After a last-start placing to the Joe-Pride trained Diamond Oasis, Brad Herne is confident Gojo Mimo will measure up in the Summer Sprint on Saturday.

But if he has any doubts about the strength of that form, the young trainer need only recall a tip from the now-retired Chris Munce, who won two races on the horse, for some assurance.

"Chris Munce used to ride him for me and he won on him one day and said `don't be surprised if he (turns out) to be one of the best sprinters in Queensland'," Herne said.

Going on Gojo Mimo's runner-up finish to Diamond Oasis in the Bat Out Of Hell Quality, Munce's claim may not be as far-fetched as it would seem for a horse barely out of restricted-grade.

Yet Herne says for Munce's crystal ball moment to come true, Gojo Mimo needs to add another dimension to what has so far been a helter-skelter approach to his craft.

"He's a very, very good 1000-metre horse," Herne said.

"But when he learns to relax a little bit he's going to be a very good 1200-metre horse."

Gojo Mimo is much better off at the weights against Diamond Oasis for a 1-1/4 length Gold Coast defeat, enough for Herne to like his chances of reversing the result.

"I know Diamond Oasis beat us the other day but we meet him two-and-a-half kilos better," Herne said.

Randwick has been downgraded into the heavy range after receiving 23mm of overnight rain with more predicted before it eases on Saturday.

A rain-affected track is likely to suit Diamond Oasis more than Gojo Mimo, resulting in the short-course specialist firming to outright favouritism.

Diamond Oasis could be one of the few remaining choice rides left at the meeting for James McDonald.

Godolphin galloper Lassitude has already been withdrawn and there are doubts over some other mounts McDonald has for the high-profile stable.

McDonald leads the jockeys' premiership by 10-1/2 winners as Sydney's riding ranks are boosted on Saturday with the return of last year's title winner Hugh Bowman who has six rides.