Gatewood skyrocketed into Cup contention yesterday with victory in the Geelong Cup.
A 1.5kg penalty would lift Gatewood to 53kg, and from 41st to 29th in the order of entry.
Manighar and Seville are ahead of him but are already out, and others would need to fall by the wayside for him to make the 24-horse field.
O'Donnell and Henderson won the Geelong Cup in 2008 with raider Bauer, who was then pipped on the post by Viewed in the Melbourne Cup.
"We are hoping for a big enough penalty to get into the Cup, and then hopefully having another crack at winning it," Henderson said.
Racing Victoria handicapper Greg Carpenter will announce the penalty today.