A vet who denies being involved in supplying cobalt could be at risk of self-harm if forced to give evidence to a Victorian appeal, a judge has heard.

Dr Adam Matthews denies fellow vet Dr Tom Brennan's claim he supplied bottles containing a substance called vitamin complex that Brennan gave to horses in Danny O'Brien and Mark Kavanagh's stables.

A judge is deciding whether to force Matthews to testify at the trainers' appeals against their cobalt disqualifications.

Matthews is suffering from a significant psychiatric disorder that requires ongoing treatment in hospital, the Victorian Civil and Administrative Tribunal heard on Friday.

Matthews' lawyer Nicole Spicer said a psychiatrist had diagnosed the vet as suffering from a significant depressive disorder.

Spicer said the psychiatrist was convinced any involvement with the legal system in the next six months would damage Matthews' treatment and welfare, including a risk of suicide.

"Having a professional of that standing identifying a genuine risk of self-harm or the taking of a person's life is not something to be taken lightly," Spicer said.

Spicer said Matthews is currently an in-patient in hospital receiving psychiatric care that includes daily treatment with a method she understood to be somewhat analogous to electroconvulsive therapy.

It would be a concern if he was compelled to give evidence during his treatment, she said.

Spicer said Matthews and his legal team agreed to him being independently assessed, although the hospital will not allow that to happen while he is an inpatient.

VCAT president Justice Greg Garde said Brennan's credibility was a significant issue in the appeal and Matthews' evidence was also significant.

"His evidence goes to the core of some of the important matters in dispute in this proceeding," Justice Garde said.

The Racing NSW Appeal Panel found Matthews not guilty of being the supplier of cobalt in a bottle of vitamin complex Brennan sent to Kavanagh's son, Sydney trainer Sam Kavanagh.

Matthews gave evidence to the NSW stewards' inquiry, after initially declining to appear on medical grounds.

Spicer suggested VCAT could use transcripts of Matthews' NSW evidence and his blanket denial that he had anything to do with cobalt or the vitamin complex bottles.

Justice Garde will decide on September 19 whether Matthews has to give evidence after hearing further submissions.

If a summons to appear is enforced and Matthews then fails to attend VCAT, a warrant could be issued for his arrest.

* Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14 or Suicide Call Back Service 1300 659 467.