Trainer Richard Gibson has no doubt Gold-Fun is good enough to win Saturday’s Diamond Jubilee Stakes at Royal Ascot but fears more rain could ruin what has been a perfect preparation for the veteran sprinter.

Gold-Fun is officially the highest-rated of 10 runners entered for the prestigious Group One sprint, but Gibson will be nervously watching the skies with showers predicted to hit the track.

The Ascot surface had been rated slow, but was upgraded to good to slow on the straight course on Friday morning, yet was still described as “tacky” by riders after day three of the five-day meeting.

Gibson’s seven-year-old won on ground rated good to yielding as a young horse in Ireland but has since encountered only comparatively rock hard tracks at Sha Tin in 28 subsequent starts.

“If we get more rain, it would be a major negative,” Gibson said. “The horse has absolutely thrived, every day has been positive and we are delighted with his physical condition. The only thing that could throw a spanner in the works is the weather – the track was OK on Thursday, just, but all you need is one decent shower and we would be out of the ball park. The ground was borderline, but we don’t want any more rain – for us the conditions are on a knife edge.”

Gibson had planned to race Gold-Fun 12 months ago at the royal meeting, where owner Pan Sutong’s electronics firm is a sponsor, but arthroscopic surgery ruled out that trip.

Gold-Fun has been consistent this season in a more well-spaced campaign geared around sprints, but has perhaps been a little short of his absolute best and the question remains: has this first overseas tilt come one or two years too late?

“That’s the big query,” Gibson said, although the Englishman, who is chasing a first Royal Ascot feature win, says the undulating 1,200m straight course could bring about an improved performance for a horse who first made his name over 1,400m and at a mile.

“I remain convinced that he will be suited by the straight track. Back at Sha Tin, the 1,200m on the flat surface has become a touch too sharp for him. He is still finishing his races off there but he just isn’t fast enough.”

What Gibson doesn’t doubt is that Gold-Fun’s best, should he be able to produce it, is good enough for him to become the third Hong Kong-trained Royal Ascot winner after Cape Of Good Hope won the same race when it was held at York in 2005 and Little Bridge won the King’s Stand Stakes in 2012.

Gold-Fun has drawn gate five, with Christophe Soumillon aboard, against nine runners including last year’s winner Undrafted, impressive last start winner The Tin Man and Godolphin’s Australian visitor Holler.

“I don’t think any of them could come to Hong Kong and beat our best sprinters, but we are playing away from home and it is up to us to run up to our rating on foreign track conditions,” Gibson said.