McInnes, a 51-year-old research fellow at the University of Edinburgh, arrived on an easyJet flight at Geneva airport on September 9th bound for a computer science conference in Martigny.
He was last seen buying a train ticket but failed to arrive at the conference and did not board his return flight home, according to police.
Writing on a blog and reported by Edinburgh newspaper The Scotsman on Tuesday, his father Bennet McInnes speculated whether his son may have been violently robbed or that a “traumatic experience” sparked a bout of amnesia.
McInnes said: “Was he robbed of his possessions, perhaps violently, and forced into confusion? He is short-sighted and always wears glasses.
“If he lost his glasses, he would be extremely disoriented and upset. If he has suffered a traumatic experience he may have lost his memory as well as his means of identification.”
Asked to consider whether his son may have intentionally taken “time out”, McInnes said: “I cannot rule out the suggestion that he has taken time out by deliberately going missing, but this seems highly implausible to me.”
He added: “We are looking for the truth. We are hoping for a good outcome, but there is much that is bad in the present situation. I believe that in the long run truth will replace ignorance.
“I hope his relatives and friends can remain hopeful till the truth about Fergus’s strange disappearance is known.”
There have been several reported sightings of Fergus McInnes since his disappearance but so far all have come to nothing.
In a statement police described him as 170cm tall, of medium build, with red hair and beard, wearing glasses.
Anyone with information should contact Valais cantonal police on 027 326 56 56