The Offer has maintained Sydney Cup favouritism after the barrier draw with confirmation the Group One staying test is almost certain to be run on a rain-affected track.

The Gai Waterhouse-trained The Offer, winner of last Saturday's Chairman's Handicap in heavy going, remained a $2.80 favourite after coming up with barrier eight.

The Offer has four wins and a placing from five heavy track starts.

Randwick was rated heavy on Tuesday and only minimal improvement is expected before Saturday's meeting.

"I think the best we could get to is probably a slow track," Randwick track manager Nevesh Ramdhani said.

Sertorius firmed from $9 to $8 after coming up with barrier three but co-trainer Jamie Edwards will monitor the track condition just as much as his horse before confirming a start.

The Zipping Classic winner has had the grounding for the 3200m, coming off a fourth in the Group One BMW and the same placing in last Saturday's Chairman's Handicap.

But the Chairman's Handicap run showed Edwards Sertorius wasn't at his best in genuinely heavy going while The Offer relished the conditions.

"I think if it's a heavy track, Gai Waterhouse's horse (The Offer) will start a very short-priced favourite and probably win accordingly," Edwards said.

Edwards said Sertorius came through last week's run unscathed and appeared to be at the top of his game.

"I'll be getting a blood taken out of the horse on Friday and if that comes back the same as what it has been the past few weeks we'll press on to run," he said.

"(But) if the track is in the same condition as it was last Saturday, I'll have to have a good discussion with the owner as far as risking the horse on such a heavy track."

The Peter Snowden-trained three-year-old Tupac Amaru, second in the Australian Derby, has has barrier nine.