Ric McMahon will have a half kilogram buffer if he needs it after dieting to get to lightweight chance Risk Aversion's 52kg in the Coolmore Classic.

Stewards have granted permission for McMahon to ride the mare at 52.5kg if required and extended the same liberty to Dwayne Dunn if he needs to ride Star Of Giselle at 53.5kg.

It's been three years since McMahon rode at 52kg and he has strived to get to the weight because he believes Risk Aversion is worth the sacrifice.

McMahon is seeking his first Group One win aboard Risk Aversion in Saturday's $600,000 race at Rosehill.

"It's a big struggle for me to ride 52 kilos but I've had a couple of weeks to work on it when I knew she was going to get in on the minimum in the Coolmore," McMahon said.

Risk Aversion is a $26 chance in Coolmore Classic betting.

McMahon is looking forward to being reunited with Whiskey Allround in the Todman Stakes (1200m).

Whiskey Allround was rated a touch unlucky by McMahon after he finished second to Sweet Idea in the Silver Slipper Stakes (1100m) at Rosehill on March 2.

"He copped a real good smash coming out of the gates but he picked himself up quickly and wasn't afraid to race inside horses," McMahon said.