David Cameron will seek MPs’ backing to launch British military action against Islamic State (IS) extremists in Syria in the House of Commons today.
He has faced criticism for branding opponents of action “terrorist sympathisers”.
Around 110 MPs have signed a cross-party amendment against air strikes, stating the case has not been made.
RAF jets are reportedly being readied for deployment from Lossiemouth in Moray.
Speaking to BBC Scotland’s Good Morning Scotland programme, Mr Salmond said: “I think the Prime Minister’s language is an indication of desperation, because he sees that the support he thought he had is starting to slip away as his case for extending air strikes into Syria starts to disintegrate on examination.”
He said he believed the Prime Minister would secure a much slimmer majority than the 176 predicted in The Daily Telegraph newspaper.
“Some of the Prime Minister’s claims start to disintegrate like dust, like the claim for example that there are 70,000 available ground troops who are going to step into the vacuum which will be released if Daesh is forced to concede ground in Syria,” the former first minister said.
“It is just not true, it is not credible. As these claims start to disintegrate, the support for this action starts to ebb away.”
The SNP has stated its MPs will vote against Mr Cameron’s plans, while Labour leader Jeremy Corbyn has given his MPs a free vote.
Some Tory members, including John Baron, will also reject the action.
Mr Salmond rejected suggestions SNP MPs were not allowed to dissent from the party line.
“Don’t be ridiculous,” he said.
“The SNP MPs are perfectly entitled and able to put forward a dissenting point of view.”
He said the party had always been “suspicious of military adventures”, and in this case there was “no credible argument for how the UK will make a military difference”.
“What is missing is a political strategy, not the tactical bombing,” he said.