Razza suggested the World Club Championship.
There's also the Super Cup, the winners of The European Cup versus the winners of the U.E.F.A Cup.
Yugoslavia has split into six (latterly seven) countries, if Yugoslavia's won it more than once then one may be in what is now Serbia and the other in what is now Croatia.
It is equally possible, but less likely, to be one from Macedonia, Montenegro, Slovenia, Bosnia and Herzegovina or Kosovo.