The trainer’s Permian won the Dante last year before taking his place in the Epsom line-up.
And, while William Buick’s mount was unplaced at Epsom, the colt did win at Royal Ascot before suffering a fatal leg injury in Chicago.
However Middleham-based Johnston, and his team, hold Mildenberger in a similarly high regard after the horse won the Feilden Stakes at Newmarket last month under James Doyle.
The York race on May 17 remains the pre-eminent Derby trial.
“Mildenberger won well at Newmarket. He really stuck his head down and galloped out to the line and the first two were six lengths clear of the third,” said Johnston’s son and assistant Charlie.
“The way he finished off that race he looks like he is crying out for a mile and a quarter and a mile and a half in time. If he can go to the Dante and run well then we can dream of going to Epsom in June.”
Johnston jnr added: “Through the winter I did say on a few occasions when people were around the yard if we were going to have another Permian this would be the horse.
“I loved him at two and he was a very nice horse at that stage, but we always knew whatever he did last year he was going to better this year as he is a huge, big, scopey horse. We always hoped he might be able to follow in Permian’s footsteps to some degree.”
The team have not yet given up hope of Dee Ex Bee earning a shot at Derby glory after finishing third at Epsom last week.
Johnston said: “If we could have our time again we would ride the race differently. James (Doyle) said he was slowly away and that meant he was a lot farther back than you would have liked.
“He has got an entry in the Newmarket Stakes on Saturday, but the likelihood is that he will go for the Chester Vase or to Lingfield for the Derby Trial.
“He is really looking already that he wants a mile and a half. In the back of our mind we are half-thinking of the Queen’s Vase and the St Leger.
“In the short term, he will be campaigned with the hope of getting him to Epsom,” he added,