The son of Frankel won the Group 1 Grand Prix de Parisbefore finding only Luxembourg too strong in a thrilling renewal of this event last season.
He subsequently finished midfield behind Alpinista in last year's Qatar Prix de l'Arc de Triomphe and wasn't disgraced when seventh in the Grade 1 Japan Cup at Tokyo.
It was then 259 days until Onesto made his next outing when fourth behind Inspiral in the Prix du Haras de Fresnay-le-Buffard Jacques le Marois at Deauville last month, with that encouraging effort likely to have put Fabrice Chappet's stable star as he attempts to gain a second Group 1 prize this weekend.
John Hammond, former trainer and now manager to Gerard Augustin Normand, owner of Onesto told Nick Luck Daily: "He goes there as a fresh horse, he picked up an injury earlier on the year which kept him off until August,"
"He ran a lovely race to be fourth at Deauville and he worked extremely well on Saturday."
Onesto looks set to face the likes of Epsom Derby winner Auguste Rodin and Royal Ascot winner King Of Steel and Hammond is certainly realistic about the challenge that lies ahead.
He added: "It's always a difficult race, as always, it's going to be a highly competitive race. You've got the likes of Auguste Rodin, King Of Steel and Nashwa."
Although it was officially soft ground at Leopardstown last year, the forecast quicker surface this year looks sure to suit Onesto.
"He looks like he's going to get his ground. The weather is set fair, and he likes top of the ground.
"He ran a great race there last year and I think he's going to go there with a good shot."
Cristian Demuro partnered Onesto when fourth in the Prix du Haras de Fresnay-le-Buffard Jacques le Marois on his reappearance, but with the French-based jockey claimed to ride on home soil for retained trainer Jean-Claude Rouget, Frankie Dettori has been booked to take the ride on his swansong season.
"Cristian [Demuro] has been claimed to ride for Jean-Claude Rouget in France that day. He's retained by Jean-Claude so that's the way that goes and Frankie [Dettori] rang up for the ride.
"We're obviously delighted to have him onboard. He's riding fantastically well with heaps of confidence and knows the track really well, so it's great everyone is delighted," said John Hammond.
Onesto is a 6/1 chance to go one better in the Irish Champion Stakes on Saturday with Paddy Power. The same firm make King Of Steel their 11/8 market leader for Roger Varian and AMO Racing.
