York winner Middle Earth will be supplemented for the St Leger at Doncaster on 16 September.
Owners Qatar Racing will pay the £50,000 supplementary fee to add Middle Earth to the field, which already contains three possible candidates from the Gosden yard - Gregory, Arrest and Lion's Roar.
Runner-up on his first two outings, Middle Earth broke his maiden over twelve furlongs at the July Course at Newmarket in late July. The Roaring Lion colt justified market support when winning the 1m6f Melrose Handicap by one-and-three-quarter lengths at the York Ebor Festival. It was the three-year-old's first attempt over 1m6f.
"He's progressed well throughout the year, he's always looked like a nice staying colt in the making," said co-trainer Thady Gosden.
"Of course, he won the Melrose, which is an impressive handicap, in good style.
"He's got plenty of size and scope, he's a horse that's taken time to mature, as many three-year-olds do.
"It's a fortunate position to be in, to have a few horses who could take up starting positions in the St Leger."
Paddy Power, Sky Bet and Betfair have all introduced Middle Earth to the St Leger market at 9/1.
