Professor Carlos Closa of the European University Institute in Florence reckons how Scotland re-enters the bloc - and on what terms - will depend on "unforeseeable circumstances" across the continent.
However, he believes that the leaders of member states with their own secessionist movements or border disputes, such as Spain, Italy, Hungary and Romania, would try to make sure Scotland is both the first and last region to secede from an EU country but stay in the EU.
Right now the possibility of part of a member state seceding and rejoining the club is not even addressed in European treaties. This has not happened since Algeria - a province of France rather than a colony - became independent in 1962, when the European common market was in its infancy.
Mr Closa said: "Scotland has a very good position because it is the first one in the line.
"But there is real fear of a domino effect across Europe, and not just in Spain's Catalonia or Basque Country. There are other member states which fear Scottish independence might trigger some kind of claims in their own territories. Italy, France and Hungary, for example, have minorities within their borders.
"After Scotland you may expect moves to prevent other member states splitting apart. Even if Scotland gains recognition and becomes a member state you will see other countries will want to foreclose this option for future territories. There is no appetite in the EU for artificially increasing the number of member states."
Mr Closa's prediction, if true, would be a particular blow for Catalan authorities, who plan an independence referendum in November but have been told by Madrid that this vote will be illegal and that any bid by the firmly Europhile Catalonia to rejoin the EU would be blocked. The UK Government, in contrast, has said it would respect the outcome September's referendum and has given no indication that it would oppose Scottish EU membership.
Mr Closa stressed the rump British state's attitude to Scotland would be crucial. But he said there was no way of knowing for sure if any of the other 27 states would cause difficulties with membership.
This, he said, could have nothing to do with Scotland. For example, another country may look to pursue its own changes to EU treaties if they are being amended to allow Scotland back in to the bloc.
Mr Closa does not expect Scotland to be forced in to the Euro or Schengen border deals. He did, however, repeat growing warnings that Scotland would not keep a share of the UK's current EU budget rebate. "There is no right to a rebate. It is just something the UK has negotiated."