French trainer Mikel Delzangles is facing a heavy disqualification over a possible race-day treatment allegedly administered to his Melbourne Cup champion Dunaden before Tuesday's race.

Acting on a report from a security guard at Dunaden's stable, stewards at Flemington opened an inquiry into the incident in which Dunaden had a paste administered before coming to the track to run in his third Melbourne Cup.

The stewards accepted the paste contained no banned substance and allowed the horse to take his place in the field.

But RVL veterinary steward Dr Brian Stewart said in his opinion the administration of the paste constituted a race-day treatment of the type that attracts a mandatory six-month disqualification.

Delzangles told the stewards he regarded it as equivalent to giving the horse food.

He said it was a treatment to combat acidity in the horse's stomach.

The inquiry heard Dunaden's groom told the security guard he planned to give the horse the paste in question and he believed the guard consented to him using it.

But the guard said he had told the groom not to administer it.

The stewards also inquired into the application of an antibiotic paste to the feet of the Gai Waterhouse-trained Tres Blue who is stabled in the same complex as Dunaden.

After hearing evidence they agreed Tres Blue could also run in the Cup, but Waterhouse is facing a similar inquiry to Delzangles.