Caulfield Guineas winner All Too Hard is not yet a certain runner in the Cox Plate with connections warning he could miss the race.

Co-trainer Wayne Hawkes said there was "every chance" the colt would run in the country's supreme weight-for-age test, but cautioned supporters to wait until a decision is announced.

"Nothing is certain, no jockey has been booked ... we won't be rushing anything," Hawkes said.

Hawkes' comments are in line with the decision of Guineas-winning jockey Dwayne Dunn to abandon a bid to shed around 4kg in order to ride All Too Hard at 49.5kg.

"It was just going to be too hard for me," Dunn said.

A decision not to run would also tally with the previous form of the stable.

In 2001 the champion colt Lonhro scored one of his finest wins in the Guineas only to be immediately sent to the paddock.

The Guineas win was the fifth of his spring preparation, while All Too Hard has raced four times since resuming with his third placing in the San Domenico Stakes on August 18.

In Lonhro's case the decision to miss the 2001 Cox Plate may have been an example of great foresight.

The horse who was an unquestionable superstar in every other sense, failed in his two runs in the Cox Plate, the second of them in 2003 when the $1.60 favourite.

There are more certain plans about the horse All Too Hard defeated in the Guineas.

Sydney jockey Corey Brown has been booked to ride Guineas runner-up Pierro in the Cox Plate with Craig Newitt scoring the mount on his Gai Waterhouse-trained stablemate Proisir, second to It's A Dundeel in the Spring Champion Stakes.

Singapore-based Brazilian Joao Moreira is among the names being mentioned to ride All Too Hard.

Clearly the best jockey in the island state, Moreira has ridden winners for Tinkler in Australia and is a natural lightweight.

Australian Stephen Baster, a clear second to Moreira in the Singapore premiership, has also put himself forward for the ride with Chris Munce also in the mix.

Conjecture surrounding Saturday week's $3 million race has resulted in Pierro easing to $3.60 from $2.90 on Sunday and $1.85 before he ran in the Guineas.

Green Moon is second pick at $4.80 with Ocean Park at $5.50 and All Too Hard solid at $10.