A man accused of mowing down pedestrians along Bourke Street in Melbourne in January may use mental impairment as a legal defence, the Victorian Supreme Court is told.

James (Dimitrious) Gargasoulas, 26, was charged with six counts of murder and 29 charges of attempted murder over the rampage on January 20.

He was accused of deliberately driving a car into pedestrians at Bourke St mall before police shot at and wounded him.

Defence barrister Theo Alexander told the court mental health experts would assess his client and, depending on their assessments, mental impairment could be raised as a defence.

"His state of mind and fitness to stand trial are real issues," Mr Alexander said.

"We have made approaches to appropriately qualified experts and are arranging assessments."

The case is still before the Magistrates' Court but came before Justice Lex Lasry for a progress update.

While murder trials end up before the Supreme Court, it currently has no jurisdiction over this case.

Director of Public Prosecutions John Champion SC said mental impairment had been raised in the Magistrates' Court for separate charges against Gargasoulas that are unrelated to the Bourke St deaths.

"There is the possibility of mental impairment being run in that court," Mr Champion said.

"If that is raised in the homicide cases, then the sooner the (Supreme) Court is involved, the better."

Justice Lasry said he was concerned the case would not reach trial until 2019 if a pre-trial committal hearing was scheduled for early to mid 2018.

"From the court's point of view and the public's point of view, that would be unacceptable," he said.

"The next thing you know 2018 is gone and the matter is still languishing in the list."

Mr Champion also told the court that police had completed more than 90 per cent of its case, but the investigation had taken longer than hoped.

Gargasoulas did not appear in court, but his case is scheduled to return to the Supreme Court in November.

ABC/AAP