Jockey Robbie Fradd has blamed a head knock for the defeat of heavily supported favourite Impregnable at Doomben.

Impregnable, backed from $1.60 to $1.40, never looked a winning hope before labouring into third place behind the winner High Cost ($10) in the Eloise Gannon Foundation Handicap.

Fradd told chief steward Alan Reardon that Impregnable had bumped his head in the stalls and failed to muster speed.

"I wanted to be up outside the leader but that was never going to happen," Fradd said.

"He was well off them in the middle stages and ran on like a horse wanting 1200 metres."

High Cost continued the good recent run of apprentice Ruby Ride.