The vet at the centre of cobalt inquiries in two states says he was merely a go-between in arranging a meeting between Mark Kavanagh and his son Sam attended by senior NSW racing official Matt Rudolph.

Tom Brennan, who has a long-standing friendship with Rudolph, has denied being a party to trying to force trainer Sam Kavanagh to change his evidence that Brennan was the source of a bottle found at his stable which was found to contain high levels of cobalt.

Kavanagh, his Melbourne-based father Mark and Rudolph had a heated meeting at a Sydney hotel with Sam Kavanagh saying he felt ambushed as the pair tried to get him to retract what he told stewards.

Rudolph, the Australian Turf Club executive general manager - racing, has been asked to show cause why he should not be penalised for his conduct.

Brennan told a Racing NSW sub-committee on Thursday, the meeting was at the behest of Mark Kavanagh who is facing cobalt charges of his own in Victoria.

"Mark Kavanagh approached me and asked me if I could call Matt Rudolph on his behalf," Brennan said.

"I knew it was regarding his son.

"Mark Kavanagh went up there (Sydney) to protect his own career.

"Matt was never meant to go to the meeting. He was to pick Mark Kavanagh up from the airport and take him there."

Rudolph has previously told the hearing he and Mark Kavanagh had coffee before he took him to meet his son.

He said Mark Kavanagh then called him back to help out after Sam became agitated.

Sam Kavanagh said he was distressed during and after the meeting on March 2.

A week earlier he had called Brennan and said he was going to name him as the source of the bottle stewards found when they raided Kavanagh's stable, labelled Vitamin Complex.

"He said `you are a non-licensed person and there's nothing they can do to you'," Brennan said.

"I said `I'm not going to cop that'."

After the meeting, Sam Kavanagh sent Brennan a text saying: "Getting Matt to risk his job. Smart play mate.

"If my daughter grows up without a father I hope you can sleep at night."

Laurie Macri, the ATC vice-chairman was also called as a witness on Thursday.

Macri, who raced Atlantic Jewel with Mark Kavanagh, said he had a meeting with Sam Kavanagh after the trainer was told Midsummer Sun had returned a positive test to caffeine,after his win in the Gosford Cup.

Macri also spoke to Rudolph after the meeting with the Kavanaghs and said Rudolph told him it was Mark Kavanagh who arranged it.

Midsummer Sun also returned high levels of cobalt in his post-race test, sparking the far-reaching inquiry.