Santiago will lead a three-strong team for Aidan O’Brien in the Pertemps St Leger – with Tiger Moth set to head elsewhere.
Irish Derby winner Santiago is set to be joined at Doncaster on Saturday by Dawn Patrol and Mythical.
Tiger Moth, a fast-finishing second to Santiago in the Curragh Classic, has options at Irish Champions Weekend – or could even join stablemate and Investec Derby winner Serpentine in the Grand Prix de Paris.
“We’re going to run three at Doncaster – Dawn Patrol, Mythical and Santiago – that’s the plan at the moment,” said O’Brien, who has won the Doncaster classic three times since 2013.
“Tiger Moth could either go to Leopardstown or Longchamp, the Grand Prix with Serpentine or the Kilternan (Paddy Power ‘Is It 2021 Yet?’ Stakes) at Leopardstown.”
O’Brien confirmed recently that Frankie Dettori is likely to be part of his team for the classic once again – the two having teamed up for St Leger success in 2005 with Scorpion.
However, final riding plans are still to be confirmed – with William Buick, who had been mooted, likely to be in Ireland to ride Ghaiyyath at Leopardstown.
“We have Frankie booked, obviously, and I think Adam Kirby might be booked,” said O’Brien.
“But what happens is the horses will all have their tests in the next few days, and we’ll confirm everything after that.”
Santiago won the Queen's Vase and Irish Derby in a short space of time. He finished third to Stradivarius in the Goodwood Cup and hasn't been seen since. The son of Authorized is 11/4 joint favourite alongside Pyledriver for the St Leger with most firms.