Graham Avery, an honorary director-general of the European Commission and senior adviser at the European Policy Centre in Brussels, says having Scotland as the 29th member would give the EU another voice on the UN and other bodies.
Writing for the Scottish Global Forum think tank, Avery, a civil servant and EU negotiator for 40 years, says that in Europe "the Scottish debate is followed with interest, and the result of the referendum is awaited with concern".
The concern arises because Scotland is the first of three areas within EU states to hold a vote on independence, with Catalonia in Spain and Flanders in Belgium set to follow.
Although the EU has constantly redrawn its borders over the last half century, it has never experienced a member state splitting in two with both parts wanting to remain in the EU.
"Thus Scotland, and alongside it Catalonia and Belgium, pose a question for which the EU has no direct precedent," Avery writes.
He argues that the EU approach would be "initial reluctance followed by pragmatic acceptance", as the impact of a state splitting in two would on balance be neutral, as there would be no change in the EU's population or its economic size.
"This does not mean that it cannot be opposed by individual member states, in particular cases and for various reasons," he cautions.
"But it can hardly be opposed on the grounds that it weakens the EU, or is contrary to the EU's basic principles or interests."
Indeed, an extra member could strengthen the EU's hand on the international stage, he adds.
"It can be argued that the EU's weight in international affairs is increased, since it gains an additional seat in the United Nations and other international organisations."
Scottish entry to the EU has been a running theme of the independence referendum.
The SNP say it could be achieved within 18 months of a Yes vote, while Scotland was still in the UK, by renegotiating EU treaties, while unionists warn Scotland could find itself cast out of the EU and forced to reapply for membership on far tougher terms than at present.
European Commission President Jose Manuel Barroso recently warned it would be "extremely difficult if not impossible" for Scotland to join the EU as it would need the unanimous approval of all 28 members, many of whom, such as Spain, do not want to boost their own separatist movements.
Barroso also raised the possibility of a veto, noting that Spain still refuses to recognise Kosovo.
Avery points out that although the five EU states which refuse to recognise Kosovo all worry about their own independence
movements, they reject Kosovo because there are doubts over the constitutional validity of its 2008 declaration of independence from Serbia.
Avery claims the Yes and No camps both mislead. He writes: "I realised some time ago that the EU is used in the Scottish debate in a misleading way, with 'unionists' presenting the EU as a major handicap to independence, and 'independentists' adopting a simplistic approach to the EU."
Avery argues it would be "common sense" for Scotland to join the EU the day it becomes legally independent, and that it would not be in the EU's interests to force Scots out of the union then make Scotland reapply for membership.
As Avery's position is often cited approvingly by the SNP, the Welsh-born expert has been perceived as a supporter of independence. However, Avery insists he is neutral.
A Better Together spokesman said: "The president of the European Commission, the president of the European Council and the prime minister of Spain have all said that if Scotland leaves the UK, it would have to reapply to join the EU.
"This would mean a commitment to join the euro and the Schengen agreement and would, undoubtedly, spell the end of the UK's hard-won rebate. If people want to avoid all of this, all they have to do is vote to stay part of the UK."
Avery's article is at scottishglobalforum.net