Aidan O'Brien feels the six-year-old might just be feeling the effects of a demanding career that has seen him compete in many races at the highest level - not least when he won the 2016 Gold Cup at Royal Ascot.
"Order Of St George is in it (Irish St Leger), but I'm not sure he is going to make it. He is just feeling a little bit of age at the moment," said O'Brien.
That might leave Flag Of Honour as the number on Ballydoyle contender after he won the Leger Trial at the Curragh last month.
O'Brien said: "Flag Of Honour is a very honest, straightforward horse.
"He had good run in France in the spring in that trial. When he went up to a mile and a half he was very comfortable at the trip.
"He does get the mile-six well but you are never sure they will get the trip until they do it, but when he went up to it he seemed to get it well."
Amedeo Modigliani has not been seen since last year's Galway Festival and his comeback has once again been put on hold.
O'Brien said: "The plan was to get him back but he had another little setback again but he is back going again.
"We are looking to get a run into him this year and then have him for next year.
"We thought we would get a run in then a big one but it doesn't look like we are going to be able to do that."
The Ballydoyle master is considering making the Goffs Vincent O'Brien National Stakes at the Curragh on Sunday week the final start of the season for dual Group race winner and leading Investec Derby contender Anthony Van Dyck.
He said: "He can step up after that or he can finish. He has had four runs now and has that experience."
US Navy Flag's preparations for The Everest sprint in Australia, the richest race of its type in the world, stepped up a gear this week.
The July Cup winner worked at Naas on Tuesday and pleased connections ahead of his trip Down Under next month.
"He did a a half-speed over six furlongs and I was very happy with him," said O'Brien.
"He is going to quarantine on Thursday to go to Sydney.
"He had a tough early part of the season and he needed a break after the July Cup, and, to be fair, that was the right thing to do. Then this race popped up and it's worth trying with him.
"He was a very fast horse last year and the minute we brought him back to six this year we saw what happened."
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