The ex-PM said he hoped voters in the forthcoming referendum would choose to stay a part of the 28-member bloc.
And speaking to French radio, he added: "In my opinion... if the United Kingdom votes to leave Europe, Scotland will vote to leave the United Kingdom".
Earlier, the UK government tabled a motion in the House Commons setting out some of the rules for the referendum.
There had been speculation Prime Minister Cameron was preparing for a vote as soon as June if his renegotiation plans were approved by European leaders next month.
The UK government will hold a vote on membership by the end of 2017.
On Sunday, Scotland's First Minister Nicola Sturgeon said a June EU referendum would be "disrespectful" given the number of elections in May.
She also repeated her belief that a UK vote to leave the EU, but a Scottish vote to stay, would lead to an "overwhelming demand" for a second independence referendum.
Following Mr Blair's radio interview, SNP MP Stephen Gethins said his party believed it "unacceptable for Scotland to be dragged out of the EU against its will".
He added: "If Scotland is taken out of the EU against its will then obviously there will have been a fundamental breakdown in what should be a partnership of nations and it is highly likely that this would trigger an overwhelming demand for a second Scottish independence referendum."
Tony Blair has said he thinks Scotland will leave the Union if the UK votes to break away from the European Union.