Except for Winx turning up as an odds-on favourite, Doncaster Mile planning for Happy Clapper and his rider couldn't have been smoother.

"I'm disappointed to have Winx in the race," jockey Brenton Avdulla said.

"I was hoping she wouldn't be there and if that was the case Happy Clapper would nearly be favourite."

As Happy Clapper has steadily gone about his lead-up work to the $3 million race at Randwick on Saturday, Avdulla has also been on a journey.

Happy Clapper earned his Doncaster berth with his Villiers Stakes win in December and Avdulla has made sacrifices to keep the association going.

By the time he goes out for the famous mile race, Avdulla will have shed 5kg - only the second time in his career that he has gone to such drastic lengths to ride a horse.

"I've only ever done the weight once in my life and that was to ride Panzer Division in the George Main Stakes a few years ago," Avdulla said.

Happy Clapper is a five-year-old but he will be one of the least experienced horses in a race in which Winx has a mortgage on favouritism as she chases her ninth successive win.

"He has been pretty much the Doncaster horse for me since the Villiers," Avdulla said.

"As long he came back and his first-up run was good he was always going to be my Doncaster ride and I thought he was worth (losing weight) for."

Avdulla rode on Thursday weighing in at 51.5kg and he felt strong.

"I've been doing it for three weeks and I've been in boot camp for probably the last week solid," he said.

"I'm within striking distance, I'm feeling good."

Winx is poised to start as one the Doncaster Mile's shortest-priced favourites after firming from $1.85 to $1.80.

Happy Clapper is a $12 chance with Winx's stablemate, last year's winner Kermadec, on the second line of betting at $8.

The Randwick course proper improved into the soft range on Friday and a further upgrade is expected when a rating is given out on race morning despite less than ideal drying conditions.

"There has been a fair bit of moisture and it now takes a bit longer for that moisture to dry out of the ground," track manager Nevesh Ramdhani said.

Avdulla has bookings in each of the four Group One races on Saturday, but his ride on Libran in the Chairman's Handicap promises to be just as important.

He has ridden Libran to win his past two starts and a third will cement the stayer's position at the top of Sydney Cup betting.