Geoff Aberdein, who served as Mr Salmond’s chief of staff during his time in office, has revealed he met Ms Sturgeon’s aide Liz Lloyd twice in March last year.
At the second meeting in late March he said Ms Lloyd confirmed “she suspected the Scottish Government had received an official complaint about Mr Salmond”.
Mr Aberdein said: “She made clear she did not know the full details of any potential complaint and had not alerted the First Minister to her suspicions about a potential complaint.”
Mr Salmond strongly denies the allegations, which date back to his time in Bute House.
Ms Sturgeon has already told MSPs she only became aware of the claims when she met her predecessor at her house on April 2 last year.
Mr Aberdein spoke out after a spokesman for the First Minister complained there had been an “attempt to smear” Ms Sturgeon with suggestions she was aware of the sexual misconduct probe before her meeting with Mr Salmond.
Questions have been raised both about Ms Sturgeon’s involvement in the probe and the Scottish Government’s handling of the investigation after it was forced to settle a court case brought by Mr Salmond.
Mr Aberdein confirmed as “a long-standing associate and friend of Alex Salmond” he had acted as an intermediary to set up the meeting with the First Minister on April 2.
He added he and Ms Lloyd both attended this but were not “party to the private conversation between Nicola and Alex”.
The former Salmond aide stated: “In the interests of transparency, this followed a request by Liz Lloyd, the First Minister’s chief of staff, to meet with me.
“This meeting, which took place on March 6 2018, was an informal discussion between friends and any reference to Alex Salmond in that discussion was in the context of media enquiries made around the time.
“Liz later confirmed at a meeting between her and I in late March, again at her request, that she suspected the Scottish Government had received an official complaint about Mr Salmond.
“She made clear she did not know the full details of any potential complaint and had not alerted the First Minister to her suspicions about a potential complaint.”
Mr Aberdein stressed: “I will not be making any further media comment on the issue.”