The Holyrood probe into Michael Matheson’s £11,000 data roaming bill is expected to reveal that he misled Presiding Officer Alison Johnstone, according to reports.

Scottish Tory leader Douglas Ross said if the allegations were accurate it would be “unforgivable” and would “raise serious questions” about the SNP veteran's future as an MSP.

Mr Matheson resigned on Thursday morning, hours before he was given a copy of the initial findings of the Scottish Parliamentary Corporate Body (SPCB) investigation.

According to the Times, it is understood their report will suggest the former health secretary misled Ms Johnstone and David McGill, Holyrood’s chief executive.

READ MORE: Tories demand Holyrood release findings of Matheson probe

Asked about the claims, Mr Ross said: "That is an extremely serious allegation and if that has occurred - there is a level of trust that there must be amongst MSPs and amongst the public who we serve.

"And if we have one of the most senior members of government at the time misleading the presiding officer of the Scottish Parliament, then it would be appalling. It would be unforgivable, and does raise serious questions about his future in politics."

He added: “I think there is an extremely strong case for the standards committee, or any other mechanism, to look at Michael Matheson’s conduct, not just as a government minister but as an individual, now backbench, MSP.

“If there is new evidence that’s come to light, that is extremely serious.”

The Herald: Douglas Ross answers questions after making a speech in Edinburgh

The Scottish Tory leader also called on Mr Matheson to hand back his £12,712.25 severance pay.

He said the public would be “outraged” if the ex-minister took the money.

READ MORE: Michael Matheson to get £13k golden goodbye after quitting over £11k iPad bill

He said: “It’s very important Michael Matheson refuses to take his severance payment – that’s over £12,000.

“I think the public would be appalled if he were to accept that money given the way he continued disgraced in office for several months and the way he finally had to resign.

“I hope that he at some stage in the whole sorry saga does the right thing and either refuses to accept that money or pays it back.”

Last year, Mr Yousaf insisted his former health secretary was a man of integrity and honesty, who had made a mistake. But following his resignation, the First Minister said it was right that Mr Matheson steps aside to avoid the issue becoming a “distraction”.

Arriving at NFU Scotland's spring conference in Glasgow on Friday, Mr Yousaf told journalists: "He's served this country and served this parliament for decades. He asked for due process - an investigation - to take place. That investigation is drawing to a conclusion, he wrote to me to say he was going to stand down and I accepted his resignation."

Mr Matheson has been approached for comment.