Joseph O'Brien believes his future as a jockey could be over jumps because of problems with his weight.
Last season's joint champion apprentice on the Flat in Ireland has had a remarkable season so far, winning his first Classic on Roderic O'Connor trained by his father, Aidan, in the Irish 2000 Guineas.
Yesterday the 18-year-old partnered 20/1 shot Reply to victory for the Ballydoyle stable in the valuable Weatherbys Insurance £300,000 2-Y-0 Stakes at Doncaster and tomorrow he rides Seville for his father in the world's oldest Classic, the Ladbrokes St Leger.
However, he is facing a constant battle with his physique and expects to be riding under National Hunt Rules at some stage in the future.
"My weight is not too bad at the moment," he said.
"I can do 9st comfortably and we'll see how long I can go.
"I would like to ride over jumps in the future, definitely.
"I am tall and I'm not going to get any lighter, so I'll see how it goes."
Paddy Power are giving odds of 16/1 that O'Brien will be champion jumps jockey in Ireland in the next five seasons, 2011-12 to 2015-16 inclusive.