Aidan O'Brien believes US Army Ranger will have to take another step forward if he is to maintain his unbeaten record in the MBNA Chester Vase on Thursday.

Despite having not raced as a two-year-old, the son of Galileo was promoted to ante-post favourite for the Investec Derby after making a winning debut at the Curragh last month.

Should the three-year-old, who is one of two entries for O'Brien along with Port Douglas, claim this Group Three prize and go on to win at Epsom, it would see him follow in the hoofprints of 2013 Derby winner Ruler Of The World who took the same route.

O'Brien said: "He is only a baby and has always been a very laid-back horse at home. He will have to learn a lot at Chester in a short space of time.

"He only won a soft maiden on very bad ground at the Curragh going a snail's pace.

"He is going to be racing around those bends at Chester which will be much quicker. At least we will see how he handles a turning track."

Karl Burke expects Biodynamic to improve for the step up in trip to 12 furlongs on his first venture into Pattern race company after finishing third in a sales race over a mile and a quarter on his seasonal return at Newmarket's Craven meeting.

The Leyburn handler said: "I am looking forward to running Biodynamic and it is not often I say that about horses going to Chester as it is not my favourite track.

"He is a progressive horse and it is another step on from Newmarket, but he has come on for that run.

"I was fairly hopeful he would pick up prize money at Newmarket but I think the winner that day, Linguistic, is a useful animal.

"He stayed on very well at Newmarket and I think he will get the trip and although the ground will be a bit quicker, he is a good moving horse and I don't think he is dependant on slower ground. Good ground should be fine.

"More importantly he has learnt from that race and he looks sharper mentally."

Charlie Hills is to monitor the ground situation before deciding if High Grounds will take his chance having also left him in the Betdaq Dee Stakes at the track 24 hours later.

After making a winning debut at Lingfield in January, the son of High Chaparral finished third in a Group Three contest at Sandown on his first start on turf last month.

Hills said: "We have decided to leave him in the Dee Stakes as well. If the ground is on the softer side, we will wait for the ground to dry out for Dee Stakes on Friday.

"If he does run in the Vase, I think the horse will stay. I think the Classic Trial at Sandown was a very good race to be honest.

"I was pleased enough as it was only the second start of his career and he was placed in a Group Three. He has gone up in the weights for that so he is on the up.

"I just felt the ground went against him at Sandown and he didn't quite handle it. I think he will be fine around Chester.

"Obviously, US Army Ranger is Derby favourite and it is not the end of the world if we finish second to him."

The six-runner field is completed by Dwight D from the yard of William Haggas and the Andrew Balding-trained Ormito.