Frankel's team admit the threat he faces in Saturday's Qipco Champions Stakes at Ascot will be his toughest test to date when he comes up against last year's winner Cirrus Des Aigles.
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The prospect of soft ground has put strains of fear into many of Frankel's huge army of followers, especially as the French raider is at home in testing conditions.
Whereas Frankel only ran for the first time over 10 furlongs in the Juddmonte International at York, Cirrus Des Aigles is as battle-hardened as they come - a fact which has not escaped Teddy Grimthorpe, owner Prince Khalid Abdullah's racing manager.
He said: "Cirrus Des Aigles has proved himself after the last two or three years.
"He's the defending champion and he came out at Longchamp and was very impressive in the Group Two.
"Certainly he's going to be a horse to be reckoned with."
Frankel does have one piece of form on soft ground, however, and whilst it was only in a maiden on his racecourse debut, he did beat John Gosden's subsequent multiple Group One-winner Nathaniel, who renews rivalry on Saturday for the first time since that race.
"He did it on soft first time out and has run on a variety of conditions," said Grimthorpe.
"He worked the other day on the racecourse at Newmarket, it could be described as soft that day, Shane (Fetherstonhaugh, work rider) got off and said he handled it very well."
Frankel's trainer Sir Henry Cecil has been fighting cancer throughout the summer but he has barely missed a morning on the gallops.
Perhaps ominously for his rivals, the 10-times champion trainer thinks the best horse in the world may be still progressing.
"I was very pleased with Frankel's final piece of work. He gives the impression that he is better than ever and still improving," said Cecil.
"I could not be happier with him. He seems full of himself and, considering the time of year, he is really good and healthy in his coat. He eats everything put in front of him.
"It will be a far from easy race with Cirrus Des Aigles and Nathaniel in the line-up.
"They are two good horses who will go in the ground and get the trip really well.
"They have to be really respected."
The one burning question after Saturday's race is whether Frankel will race again.
And while it is highly unlikely, a final decision has still to be made.
"It is entirely Prince Khalid's decision, he will make it in his own time," said Grimthorpe.
"He know this is a very public horse - he shares the horse with the public - but the decision is one he will make when he's ready."
In completing his perfect 13-from-13 record, Frankel sparked debate across the racing world as to which was his best performance.
Grimthorpe believes his seven-length victory in the Juddmonte International at York, when he was stepping up to a mile and a quarter for the first time, was his defining moment.
"I'm slightly biased, but I thought his last performance at York had all the ingredients for me - it was absolutely sensational," said Grimthorpe, who holds an executive position on the Knavesmire.
"As a two-year-old he started to prove himself exceptional and he's improved and blossomed into the horse we know.
"This year has proved how hard it is to get a top-class horse to the races.
"Henry has brought this horse 13 times to produce his best on 13 occasions.
"To have produced him without a blip is testament to Henry and his team."
Tom Queally has been the lucky man on board for each race but cannot pick out one particular highlight.
"York was a complete performance as he was completely professional," said Queally.
"The Guineas was breathtaking, it sort of had the 'wow' factor, but the Juddmonte and Queen Anne were equally as impressive.
"I've been in a very privileged position and he's been a huge part of my life.
"He's raised my profile and I'm delighted to have been associated with him."