Trainer Roger Varian has been buoyed by heavy rainfall at Doncaster ahead of Kingston Hill's likely tilt at glory in the St Leger.

The high-class colt is the warm favourite for the final Classic of the Flat season on Saturday but he does require ease in the ground to be at his best.

Kingston Hill was taken out of the Irish Derby at the Curragh and the Great Voltigeur Stakes at York due to unsuitable conditions, but Varian was happy to see 14mm fall at the South Yorkshire circuit on Saturday.

"The rain they had at Doncaster on Saturday was very useful for us," Varian told the Times.

Varian reaffirmed the Prix de l'Arc de Triomphe at Longchamp on October 5 may come into the reckoning if Kingston Hill runs with honour in the St Leger.

"It's no concern to me that he hasn't run for a while and I'd be keen on the Arc if all goes well at Doncaster," he said.

"I know it's never been done, winning the Leger and the Arc in the same season, but he hasn't had a busy summer and Andrea (Atzeni, jockey) got off him the other day and said he'd never felt better.

"First things first, he has to win at Doncaster, but he has an amazing constitution and could go on to a target three weeks later."