The Newmarket handler has earmarked the extended one-mile-five-furlong Group Three contest as a possible stepping stone towards an outing in the final Classic at Doncaster next month.
Since returning to action, the son of Dalakhani has won each of his three starts with his most recent victory coming in a Listed race at Hamilton.
Varian said: "Defoe is in good form. He worked well with Andrea (Atzeni) last Saturday morning. The St Leger is our big goal with him.
"We might think about running him in the Geoffrey Freer at Newbury on Saturday before that though."
The Charlie Appleby-trained Frontiersman and Brian Meehan's 2015 race winner Agent Murphy are among his possible rivals at this stage.
Defoe is a 14/1 chance with Sky Bet for the St Leger.
Chris Wall is ready to let his star filly Mix And Mingle take on the boys in the Betfred Hungerford Stakes on the same Newbury card.
The daughter of Exceed And Excel won her first two starts of the campaign, including a Group Three victory over star French filly Qemah in the Chartwell Fillies' Stakes at Lingfield. She disappointed in the Duke of Cambridge Stakes at Royal Ascot, but Wall is hopeful she can get her season back on track this weekend.
"She's been confirmed for the Hungerford and as long as we don't get a deluge of rain at the end of the week, the plan is to run," said the Newmarket handler.
"We had hoped to go for the Oak Tree Stakes at Glorious Goodwood, but unfortunately the ground went too soft, so we've just had to keep her ticking over. There was nothing for her between Ascot and Goodwood really and it was annoying we couldn't run her there.
"I think Ascot proved she doesn't stay a mile and just with the way the race was run, it didn't work out for her on the day. She'll be taking on colts on Saturday, which is not ideal, but she's in good form and we're looking forward to running her."
Mix And Mingle is one of 22 horses confirmed for the seven-furlong Group Two. Last year's winner Richard Pankhurst is in the field once again, as is 2014 victor Breton Rock, who caused a 50/1 upset in the Lennox Stakes at Goodwood on his latest appearance.
The two Irish contenders are Aidan O'Brien's Spirit Of Valor and the Ger Lyons-trained Psychedelic Funk. Other hopefuls include Kaspersky, Jungle Cat and Librisa Breeze.
