Jockey Hugh Bowman believes Newcastle-trained rival Le Romain and Chautauqua showed in the Canterbury Stakes that they were up for the challenge of taking on Winx on Saturday.
Winx, now rated equal top in the world's best racehorse rankings, will chase a 16th consecutive victory when she steps out in the $1 million weight for age George Ryder Stakes at Rosehill.
The Chris Waller-trained mare will be expected to dominate again, but Bowman believes the race will be her toughest for some time, despite her impressive build up with easy wins in the Apollo Stakes and Chipping Norton Stakes.
"She's starting to get to a level that she was when she won the Cox Plate last year, so that to me is very exciting," Bowman told AAP.
"In saying that though I think the George Ryder will probably be the most competitive event for her in some time. The fact is it's 1500 metres, so it's probably short of her best distance, and she's going to take on some serious competition in Chautauqua, Le Romain and others.
"I think those two horses put the writing on the wall in the Canterbury Stakes the other day that they're up for the challenge."
Kris Lees’ Le Romain beat Chautauqua on the line in an epic battle on heavy ground in the Canterbury Stakes on March 4.
Le Romain had his final serious hit-out before the George Ryder on the Newcastle course proper on Tuesday.
Lees was pleased with the work but said: “It would want to be good because we’re taking on the best horse in the world.”
Le Romain rose to equal fifth in the world rankings with his third group 1 victory.