Peter Snowden has described the autumn carnival-ending injury to Group One winner Complacent as a tragedy.

Complacent was one of the favourites for the Group One ATC Australian Derby but has been ruled out of the entire autumn because of a strain of a pastern.

"He was the best staying prospect I've ever had," Snowden said.

Complacent rose to prominence last spring going from a Hawkesbury maiden win in September to taking out the Group Three Gloaming Stakes and Group One Spring Champion Stakes at his next two starts.

He ended his spring campaign with a second to Polanski in the Victoria Derby after striking interference.

"It's a tragedy," Snowden said of the carnival ending injury.

"These things happen. It's not life threatening and I feel confident that it will come right with a bit of time.

"He's already started a bit of rehab work on it and I feel confident by the spring that he will be fine."

Snowden and his son Paul will start a training partnership after the Sydney autumn carnival with John O'Shea to take the reins as Darley's head trainer.

With Complacent out of the ATC Australian Derby in April, Polanski is the $3.50 TAB favourite for the 2400m Classic ahead of Savvy Nature at $6.