Tim Clark fears the handicapper might have cruelled his chances of winning a third Group One Galaxy aboard smart sprinter Famous Seamus at Rosehill on Saturday.

The gelding has 56.5kg in the 1100 metre feature and will concede weight to proven Group One performer Temple Of Boom and the flying Rain Affair, a four-time placegetter at the elite level.

Famous Seamus will be stepping out in top company for just the second time, his only other attempt being in last year's Stradbroke Handicap when he finished among the tailenders.

"I think he's pretty poorly weighted," Clark said.

"He's giving weight to Rain Affair who I know hasn't been at his best but he has been Group One placed multiple times."

The Galaxy has been a defining race in Clark's career.

He landed his first Group One triumph in the 2008 edition aboard Typhoon Zed and was again in the winner's stall three years later aboard Atomic Force.

If Famous Seamus wins on Saturday it will give Clark his sixth Group One success in Australia and half of those will have been in the Galaxy.

Despite his concerns over the handicapping, Clark believes Famous Seamus has an attractive profile.

The five-year-old has been carefully managed by trainer Noel Mayfield-Smith and the jockey saw plenty of merit in his first-up performance when he worked home strongly for third behind Galaxy rivals Villa Verde and Snitzerland in the Challenge Stakes.

It came on the back of a spring campaign in which he won a Listed race at Randwick and was Group Three placed behind Lankan Rupee in Melbourne.

"It was probably a career-best first-up run from him," Clark said of the Challenge effort.

"That is probably going to be the right form race for this."

Famous Seamus is a $12 chance with betting headed by Snitzerland who trainer Gerald Ryan has warned could be scratched if the track remains heavy.