Leading fancy Shalapour will bypass the Ladbrokes St Leger at Doncaster on September 10th and wait for the Irish equivalent a week later.
Trainer John Oxx made the decision to send the Darshaan colt to the Curragh because it gives the three-year-old more time to prepare for the race.
"We're going to run him in the Irish Leger to give him an extra week to recharge his batteries," explained the Currabeg handler.
"If we give him a bit more time that should suit him better. He's been coming along nicely in his work and we are happy with him."
Shalapour, a gallant third behind Hurricane Run in the Irish Derby, was last seen on a racecourse finishing runner-up behind Chelsea Rose in the Listed Ballyroan Stakes in August.
Oxx admits his charge was not fully wound up on that occasion, and expects further scope for progress in the Group One Irish Field St Leger.
"It was a good run last time but he wasn't at his best and should improve as he gets older," added Oxx.
"The step up to a mile and six shouldn't be a problem at all. Vinnie Roe [the winner of the Irish St Leger for the last four years] is a good horse, but we're hopeful about his chances."