A man who made an anonymous telephone call to Racing NSW stewards on the day the John McNair-trained Normandy returned a positive test to methamphetamine remains a person of interest in the matter.

The man told chief steward Ray Murrihy on March 18 that the horse had been tubed.

Normandy subsequently returned a high level of amphetamine, a metabolite of methamphetamine which has a street name of ice.

At an inquiry on Thursday, Racing NSW stewards heard evidence that the high level of the illegal drug must have been administered at least five hours before the horse raced and could not have been a result of human-to-horse contamination.

In the only other ice case heard in NSW, three horses trained by Luke Griffith returned levels of around five nanograms per millilitre of urine, while Normandy's reading was 170.

The inquiry was adjourned to allow stewards time to undertake a thorough check of telephone records.

Evidence was also taken in camera from a man employed by McNair to do work on his property.

The man cannot be named because he is involved in a civil suit with the trainer.

McNair has denied giving the horse any treatment.

"The person who made the call is a person of interest and we will be making a thorough investigation," Murrihy said.

Normandy has been stripped of his fourth placing at Newcastle on March 18.