A man who assaulted a female strapper in front of more than 60,000 people on Oaks day at Flemington is in police custody.

A registered stablehand with Darley Australia, the man king hit the young woman in the mounting yard as she was waiting to bring Black Cash back to the winner's stall after the greys race on Thursday.

The incident was witnessed by chief steward Terry Bailey, who was nearby, and also captured by the Seven Network.

The man ran off to the horse stalls, where he was caught and detained.

Darley's managing director, Henry Plumptre, refused to comment, but Bailey confirmed he was with the leading stable.

The young woman, who is believed to have known the man, had a bruised and swollen right cheek when she brought the horse back to the enclosure.

She initially refused medical treatment, but Bailey insisted and she was later taken to hospital for observation.

The man is likely to face charges from racing authorities in addition to any laid by police.