Peter Snowden is not sure if Long John is good enough to topple a field of weight-for-age stars in Saturday's Cox Plate but he is certain the classy three-year-old deserves the chance to do so.

Snowden elected to keep Long John at home at Flemington on Tuesday morning for his final major piece of work before Saturday's $3 million race rather than take him to Moonee Valley's public trackwork session.

"It's a pretty busy morning at Moonee Valley and I don't think he needed it," Snowden said.

"The work I wanted to give him, he did really well at home and I'm really happy how the horse is."

Long John earned his shot at the weight-for-age championship of Australasia with his Group One victory in the Caulfield Guineas last start.

He is aiming to become the first winner of that race since Red Anchor in 1984 to win the Cox Plate in the same year.

Snowden took 2011 Caulfield Guineas winner Helmet to the Cox Plate where he finished eighth and the trainer admitted it was a big call to try again.

"It's a big ask but these sorts of horses with the record he's got, why not give him his chance," the trainer said.

"We'll need to be at our very best but why put a cap on a horse that keeps winning?

"Who knows how far this bloke will go. He's well in himself, he's got 49-1/2 kilos on his back and we'll be out there doing our best."

The Cox Plate (2040m) will feature two three-year-olds with the Danny O'Brien-trained Shamus Award gaining a start after Tuesday's shock scratching of Atlantic Jewel.