Suspended senator Mike Duffy’s lawyer will not rule out calling Prime Minister Stephen Harper as a witness, as his client’s fraud case goes to trial.

After petitioning the court Tuesday morning to set the earliest possible trial date for his client, Donald Bayne said the defence is “considering any potential witness. It’s too early to rule anything out.”

Bayne said he will consider what is “relevant to the defence of Sen. Duffy” when deciding on a course of action at trial.

"Let me make clear, this isn't a political case, this is a criminal case… The very strong judiciary in the Ontario court of justice will not allow this case to be turned into a political circus," he told reporters. "At this point, it's too early to rule anything out. But please understand, this isn't being run as a personal or political vendetta."

Duffy is facing 31 charges including fraud, breach of trust, and bribery in connection with allegations of misspending.

A big question looming over the trial is how much Harper knew about a $90,000 payment from former chief of staff Nigel Wright to Duffy, to cover his contested Senate expenses. Harper has said on numerous occasions that he knew nothing about the payment.

During question period, Opposition Leader Thomas Mulcair asked Harper whether he will “hide behind Parliamentary privilege or will he testify” if he is called as a witness.

Harper replied: “Obviously if you read the investigator’s report, there’s absolutely no reason to suggest that I would do that. What I would say to the leader of the NDP if anyone were to ask me about the inappropriate use of public funds, I would certainly suggest him as an expert witness.”

Harper was referring to a recent decision by Parliament’s Board of Internal Economy that found the NDP inappropriately spent taxpayer dollars on satellite party offices.

Mulcair followed up by asking why Conservative staffers who appeared to have knowledge of Wright’s $90,000 payment were not fired. Harper replied that it is the NDP that has been found to misuse public funds.

“He’ll have to ask why he’s not firing himself.”

Meanwhile, Duffy’s lawyer said he is hoping to have a trial date set when he next appears in court on Sept. 23.

"The trial date is being set in the normal course… and we are going to fix the earliest possible trial date," Bayne told reporters outside the Ottawa courthouse Tuesday morning, explaining that the trial will be Duffy’s first chance to clear his name by presenting evidence before an impartial tribunal.

Because Duffy has had two open heart surgeries, Bayne said he wants the trial to go proceed quickly out of concern for his client's physical and mental health.

Duffy is waiving his right to a preliminary hearing to expedite the trial.

Bayne expects, once it gets underway, the trial will run for six to eight weeks.

With a federal election scheduled for next year, Duffy’s trial could either precede or coincide with the campaign period.

If the early date is granted, Duffy will likely be the first of three senators involved in the expense scandal to go to trial.

Another suspended senator, Patrick Brazeau, will wait until June of next year for his trial on charges including fraud and breach of trust.