A man has been warned off for refusing to co-operate with the ongoing Racing NSW stewards' investigation involving suspended Newcastle trainer Benjamin Smith.

Neil Costello has been banned immediately until such time as he attends an interview and provides information to the satisfaction of Racing NSW.

The consequences of being warned off include not being permitted to enter any racecourse or training facility, not be able to have an interest in any thoroughbred race horse and not being able to place a bet on thoroughbred races with a wagering operator.

Costello was questioned by Racing NSW stewards on Friday but left before left before the interview was concluded and contrary to the direction of stewards, in the knowledge he would be subject to sanction.

Stewards said Costello's refusal to cooperate with them had obstructed and hindered them in investigating serious breaches of the Rules of Racing.

The decision to warn Costello off was made by Racing NSW chief executive Peter V'landys under his delegated authority.

"Racing NSW is on record time and again as saying integrity in this industry is paramount. Accordingly, no individual's interest should outweigh the confidence of the public, and particularly punters, in the integrity of the industry," V'landys said.

"Racing NSW has zero tolerance for those that obstruct and hinder the maintenance of the integrity of thoroughbred racing in New South Wales."

Smith was stood down for giving false evidence regarding unlabelled and unidentifiable substances in his stable and for refusing to give evidence as to their origin.