Trainer Aidan O'Brien has confirmed Ryan Moore will increase his presence within the Coolmore operation.

The Cox Plate and Melbourne Cup winning jockey flew back from the Dubai World Cup meeting to ride for O'Brien at The Curragh on Sunday.

He replaced the trainer's son Joseph whose weight is becoming an increasingly difficult problem.

"We've a good relationship with Ryan and we always have. We used Ryan more last year than we did the year before and hopefully it will be that way again this year," O'Brien told At The Races.

"We're delighted Ryan is there and he is riding for us."

Moore will be in Sydney on April 11 to reunite with Cox Plate winner Adelaide who is being prepared for the Queen Elizabeth Stakes by premier Sydney trainer Chris Waller.

O'Brien jr, meanwhile, is set to be return to Flat racing at Dundalk on Wednesday, but his father is unsure how long he can go on battling his weight.

"Obviously nine stone (57kg) has been a problem for the last two seasons and last year it was a big problem," he said.

"This year he's heavier than he was this time last year.

"There's no doubt he'll come back down to the Flat gently and how far down he'll go, we'll wait and see.

"It's fun and enjoyment for Joseph (riding over jumps) and he loves doing it. I suppose it was me that was keeping him away all the time really."