Milligan has suffered multiple fractures to his skull and face from the incident on Saturday morning.
Racing NSW doctor David Duckworth said Milligan had been to the operating theatre to have some lacerations cleaned and sutured and would undergo further surgery to his face later in the week.
Milligan is best known for the deeds of grand campaigner, multiple Group winner Carael Boy.
Among the gelding’s 20 wins were the 2001 Group Two Villiers Stakes and the 2005 Wyong and Newcastle Cups.
Credit: AAP