The Middleham trainer also saddles Nayef Road as Stradivarius seeks a record-equally fourth consecutive victory in the blue riband Group One race.
If Stradivarius prevails under Frankie Dettori it will also be the horse’s fifth win in successive years at the celebrated meeting after taking the Queen’s Vase in 2017.
But Johnston, who is Britain’s most successful trainer, is no stranger to Gold Cup glory following the wins of Double Trigger (1995) and Royal Rebel (2001 and 2002), has high hopes for Joe Fanning’s mount Subjectivist.
The horse came to prominence when winning the Group One Prix Royal Oak at ParisLongchamp last October before landing the Dubai Gold Cup at Meydan in late March.
The worry is a lack of a prep race.
“He did have an injury in that Dubai race.
“It’s taken him a little while to come back from that and as a result we haven’t had any race in between,” said Johnston, who revealed his colt also had a fall at home recently but escaped injury.
“I think this is the best horse I’ve gone to war with Stradivarius with. We know what a tall order that is – we’ve finished second to him so many times before.
“I won’t be looking at tactics to beat Stradivarius, we’ve just got to hope that we’ve got the best horse on the day.”
Nayef Road, who chased home Stradivarius last year, will be hoping to go one better under Ben Curtis.
“Nayef Road is going to Ascot on the back of two disappointing performances, but while his second in the Gold Cup last year was with cut in the ground, we had previously always thought he was better on fast ground,” said Johnston.
“We are hopeful that on better ground we’ll see him back to his best, although there’s obviously some rain forecast.”
However, all eyes will be on Stradivarius – and the weather – after the Ascot course specialist made a winning return in the Sagaro Stakes in the colours of Bjorn Nielsen.
“He seems to love his training still, he still seems to love his racing,” said trainer John Gosden.
“He can be very naughtily behaved beforehand and think he’s in the covering shed – not at the racecourse – but when it comes to the race and he gets down to the start, he can look at a mare and think ‘OK, I’ve a job to do’.
“Touch wood, we’re ready to go again.”
Stradivarius would join Aidan O’Brien’s Yeats as the only other horse to have won four Gold Cups, and Gosden believes his first was his stiffest task when beating Vazirabad, Torcedor and Order Of St George.
“He has been remarkable. He has this exciting turn of foot,” said Gosden. “I think the toughest race of his life was his first Gold Cup against the great French stayer [Vazirabad], but overall I think his record stands up.
“His win in the Sagaro was tidy, pleasant, he [Frankie Dettori] didn’t ask him too much so let’s hope he’s ready for the big one again.
He did have one word of caution, however – the weather. “I fear one thing for Stradivarius – thunderstorms – because he has this wonderful turn of foot after two and a half miles but the wet ground, soft ground, blunts it, so we’ll see how we go,” added Gosden.
“I’ve got a lot of respect for the new boy on the block. There’s no doubt Subjectivist adds a lot of spice to the race.”