Aidan O'Brien is considering Plan B for his staying challenge this term, with reigning champion Kyprios a major doubt to defend his Gold Cup title at Royal Ascot.

The five-year-old carried all before him in the marathon division last season, winning each of six starts, including the Ascot showpiece, the Goodwood Cup, Irish St Leger and a tremendous 20-length success in the Prix du Cadran, achieved despite hanging badly across the track.

O'Brien revealed on Sunday Kyprios had suffered a setback, and he expanded on his injury issue when speaking to visiting media at his yard on Monday.

He said: "I don't think Kyprios is going to make the Gold Cup. He got a little bit of a joint and it's not settling down. We will just have to wait and see. It's one of those things.

"It happened a month ago and it's just not settled - sometimes these things can settle very quickly and sometimes they don't. He got an inner infection inside in the joint and it had to be flushed and then there was more infection, so it had to be flushed a second time."

If as seems likely Kyprios does miss out, O'Brien has identified some possible deputies, headed by Emily Dickinson - winner of the Loughbrown Stakes when upped to two miles on her final start last term.

Saturday's Dubai Gold Cup winner Broome is another contender, along with Changingoftheguard, who won the King Edward VII Stakes at Ascot when last seen.

He added: "Emily Dickinson, Broome, Changingoftheguard is a possible - even though we probably won't make a decision (yet).

"We were very impressed with Emily at the Curragh, she grew another leg when she went to two miles. I'm not sure whether Broome will stretch out that far (two and a half miles at Ascot), but you'd imagine he'll be very happy at Goodwood, Irish Leger, the Melbourne Cup, those type of races."

At the other end of the scale, Tenebrism will flex her sprinting muscles for the Ballydoyle team after trying her hand up to a mile last term.

O'Brien is eyeing an audacious Royal Ascot double, with the King's Stand and Platinum Jubilee Stakes in mind.

He said: "Tenebrism is going to go sprinting. She'll probably start in one of the local sprints, she's nearly ready to go, she was at the Curragh (on Saturday) and worked well.

"She's a fast filly, I'd say five or six she'd be comfortable at. We're thinking both with her, the five and the six - we thought she could do the two (at Ascot). We were dallying around her last year, seeing where we were going to go and but the minute we started sprinting, it was very obvious she was a sprinter.

"She'll be trained differently, last year we were trying to stretch her out and she was still being very competitive at those distances, she's just a good filly.

O'Brien also outlined some early-season juveniles, to monitor, headed by a No Nay Never half-brother to Sioux Nation.

He said: "Alabama is one to watch, Battle Cry is another No Nay Never, Emperor Of Rome, a Ten Sovereigns filly called Brighter, I think they're the more forward types. You'll not go far wrong with Alabama, who is a brother to Sioux Nation.

"The Liffey is another one, His Majesty is another No Nay Never, Carnegie Hall, they're some of the early-type ones."