OPPOSITION Leader Tony Abbott is standing by SA Liberal Senator Mary Jo Fisher, who faces charges of theft and assault.

Mr Abbott said yesterday although he "did not want to talk about private circumstances", he was aware Senator Fisher was battling depression.

"The party is right behind her and supporting her in this tough time," Mr Abbott said.

Senator Fisher was yesterday bunkered down at her Adelaide home following revelations she had been charged over an incident at the Frewville Foodland last year.

Contacted by The Advertiser she remained reluctant to talk about the charges.

Senator Nick Xenophon, who works with Senator Fisher on a parliamentary committee, said yesterday "the presumption of innocence is paramount".

"She is a particularly astute and hard-working member of the committee," he said.

"If depression is involved then we should all look at these events through this prism."

It is alleged that Senator Fisher stole $92.92 of groceries from the supermarket in December last year. She was also charged with assaulting a security guard who tried to stop her from leaving the supermarket.

She faces court on September 1.

Her colleague, Opposition finance spokesman Andrew Robb, has said the Senator is suffering from depression and anxiety.

Political analyst Haydon Manning said the fact a sitting MP was facing criminal charges was "unusual, there's no doubt about it".

"The reality is we are actually very corruption and scandal-free in Australia," he said.

Under the Commonwealth Constitution, if an MP is convicted of an offence that has a penalty of imprisonment of at least a year, they are disqualified from holding office.

About a million Australians experience depression and two million suffer some form of anxiety disorder, depression initiative Beyondblue says.

Senator Fisher entered the Senate in 2007, filling a vacancy left by the resignation of Amanda Vanstone.

She attracted attention this year for performing the Hokey Pokey and the Time Warp in the Senate while attacking the carbon tax.