Cox Plate winning jockey Ryan Moore will take the main rides for Coolmore on the opening day of the Irish Flat season with Joseph O'Brien battling his weight.

Instead of riding at The Curragh on Sunday, O'Brien, the son of trainer Aidan O'Brien, will partner Egyptian Warrior in a hurdle at Limerick.

The 21-year-old has twice been Ireland's champion Flat jockey and said he hoped to get his weight under control but admitted his long-term future was uncertain.

"I'm probably a fraction heavier than I have been," O'Brien told the Racing Post.

"I'm hanging in there and we'll see what happens over the next while. It should be stabilising now and we'll take it as it comes.

"It's always been the way with me. I can't ride forever ... and I've approached every year like that. I don't think I can look to the long term.

"I will definitely ride over jumps too, but whether I see myself as a jump jockey or not is another question."

Moore, who rode Adelaide for Coolmore to win the Cox Plate, will fly back to Ireland after riding at the Dubai World Cup meeting.