Winx in 'best shape ever': Trainer Chris Waller

Champion trainer Chris Waller has said Winx has never been in better shape, as she prepares for a tilt at a record 4th-straight Cox Plate win.

The wonder-mare will start heavy favourite in the five-million-dollar, group-1 race this Saturday at Moonee Valley Racecourse in Melbourne.

Waller said he expects a few more contenders may jump in to make up the numbers amid talk of a field of seven or eight.

"A field of eight would be perfect for us because it means less horses get in her way," Waller said.

He did not want too small a field either.

"The more pressure the better. That's when Winx performs best."

Following a stunning 28 consecutive victories, Winx's future beyond Saturday's race remains unknown.

The growing anticipation is well-timed with the launch of Andrew Rule's authorised biography on Winx's unlikely rise to stardom.

"(She's) without doubt one of the handful of greatest horses of all time - and I mean 250, 300 years," Rule told 9News today.