The Prime Minister's decision to replace William Hague as Foreign Secretary with Philip Hammond, who last year said he would vote to leave the EU unless powers were clawed back, prompted Alex Salmond to pitch the PM's ministerial shake-up at the heart of the independence referendum.
The First Minister claimed the ex-Defence Secretary's new appointment had "put one hand on the exit door leading the UK out of the EU".
But more political turbulence was caused when Perth-born Mr Fallon declared: "It's certainly a eurosceptic Cabinet, but the country is eurosceptic now."
Asked if the reshuffle contained a message aimed at Ukip supporters, he said: "We certainly want people who may have flirted with Ukip at the recent European election to understand how we can get change in Europe and understand that the Conservative Party is the only party that can deliver that change."
Later, Mr Cameron's spokesman, asked about the Defence Secretary's remarks, pointed to the PM's January 2013 speech in which he announced the proposal for an in/out referendum and claimed British public support for EU membership was "wafer-thin".
Angus Robertson, the SNP leader at Westminster, seized on Mr Fallon's remarks, saying: "He has only confirmed what we all know; the UK Government has taken a decidedly and dangerous shift to the eurosceptic hard right."
He added: "Only a Yes vote in September can secure Scotland's place in Europe, giving us a seat and a voice at the top table; Westminster is dancing to a Ukip tune and that tune is leading only one way."
Mr Fallon's remarks also ruffled Liberal Democrat feathers, with Deputy Prime Minister Nick Clegg insisting that Britain was "anchored firmly in the heart of the European Union".