Naturalism Stakes winner Mr O'Ceirin has been penalised half a kilogram for the Caulfield and Melbourne Cups for his Group Three victory.

The Ciaron Maher-trained stayer booked his place in the $2.5 million Caulfield Cup (2400m) on October 19 with his victory in Saturday's Naturalism (2000m) which carried a ballot exemption to the Caulfield Cup for the winner.

Mr O'Ceirin, however, was liable for a penalty for the win and his Caulfield Cup weight is now 53kg.

He was also given the same penalty for the Melbourne Cup will now carry 52.5kg for the 3200m Flemington feature.

He has moved from 48th to 45th in the Melbourne Cup ballot order.

"Mr O'Ceirin is a progressive stayer having won the (Listed) Grafton Cup in July and won a strong renewal of the Naturalism on Saturday," Racing Victoria's chief handicapper Greg Carpenter said.

"In determining the size of the penalty, the fact the Naturalism was slowly run in the early and middle stages and Mr O'Ceirin was assisted by a tactical front running ride mitigated against a penalty of any more than 0.5kg."

Racing NSW has announced Mr O'Ceirin has received a 1.5kg penalty for the Group One Metropolitan (2400m), taking his weight to 54kg.

Maher said after Saturday's race that the stayer would probably run in the Caulfield Stakes before the Caulfield Cup.