It's a case of don't be sad she's leaving, be happy that she was there at all for trainer Stuart Webb who is preparing to farewell triple Group One winner Yosei from his stable.

A below-par run for last in the Toorak Handicap on Saturday confirmed the mare was not racing with her usual heart and the decision was made to send her to stud while there was still time this season.

Webb, who prepares a small team along with his duties as assistant trainer to Robert Smerdon at Caulfield, said the mare was a once-in-a-lifetime horse for him.

"It is a bit sad but we knew it had to come eventually," Webb said.

"The plan had been to keep her racing until the autumn but she's told us it's time now.

"Her coat looked ordinary. If she had been beaten three lengths maybe you could find an excuse but to be beaten 12 lengths - that was too much.

"It's not too late for the owners to send her to stud so that's what they will do.

"It has been a privilege to train her. She's definitely a stable favourite and I don't know if I'll ever have a horse like her again."

Although she only won four of her 41 starts, three of those were at the highest level. Her first came in the 2010 Sires' Produce Stakes at Randwick, a win which was also history making for her jockey Michelle Payne who became the first woman to win one of Sydney's juvenile triple crown races.

Later in the year she took out the Thousand Guineas at Caulfield and the following season claimed the Tatt's Tiara during the Brisbane winter carnival.

Among Yosei's five placings were Group One thirds in the 2012 Doncaster Mile and Toorak Handicap and this year's Robert Sangster Stakes.

"Maybe one day I can train one of her sons and daughters," Webb said.