Connections of Main Sequence have yet to decide whether to renew rivalry with the Triple Crown-seeking Camelot in the Ladbrokes St Leger at Doncaster next month.
David Lanigan's stable star has already taken on Aidan O'Brien's unbeaten colt once before in the Investec Derby at Epsom in June when he stayed on well to take second place, five lengths behind the brilliant winner.
But while the 2000 Guineas hero has gone on to further Classic glory in the Irish Derby at the Curragh, Main Sequence has suffered defeat in both his subsequent races.
An unlucky fourth behind Camelot's stablemate Imperial Monarch in the Grand Prix de Paris at Longchamp in July, Main Sequence was second behind Thought Worthy in the Great Voltigeur Stakes at York last week.
The Lanigan team are toying between whether to step Main Sequence up to an extended mile and three-quarters in the world's oldest Classic on September 15, or to return to Longchamp for the Prix Niel a day later.
"He's come out of the race fine, but I still have to sit down with the owners and decide which way we're going with him," said Lanigan.
"He's in the Irish Champion Stakes, but he won't run there.
"The two options for him are the St Leger and the Prix Niel in France.
"I need to discuss things with the owners and then make a final decision."
Camelot heads the 16 remaining entries for the St Leger at the latest scratchings stage as the build-up continues to his bid to become the first horse since Nijinsky in 1970 to complete the Classic hat-trick on Town Moor.
Camelot is one of six remaining possible runners for the powerful Ballydoyle team, with Imperial Monarch, Chamonix, David Livingston, Father Of Science and Offer.
John Gosden has a well-documented strong hand, with the Clarehaven maestro responsible for five possible runners.
Thought Worthy could be joined by Irish Oaks heroine Great Heavens, Shantaram, Michelangelo and Dartford.
Thought Worthy is owned by George Strawbridge, whose his racing manager James Wigan, said: "I would say Thought Worthy is a likely runner in the St Leger.
"He put in a very gutsy performance in the Great Voltigeur Stakes last week when he really put his head down and tried.
"Dynaformers have a habit of improving.
"Thought Worthy is a lovely looking individual and physically he has come on significantly since his run at Royal Ascot.
"His brother Lucarno won the St Leger and Thought Worthy really tries and gallops so you never know."
Hugely impressive Melrose Stakes winner Guarantee could become a first Leger runner for trainer William Haggas, while Encke, Thomas Chippendale and Ursa Major complete the high-class list.
