Rune Andersson was stopped by two men, one of whom was wearing a police uniform, on Sunday afternoon near the southern town of Mostar. The two beat him up and took his car, leaving him handcuffed near the road, where he was found the next morning.
The head of European Commission delegation, Michael Humphreys, condemned the attack and called for a speedy investigation to bring the assailants to justice.
The EU is assisting Bosnia in undertaking reforms aimed at stabilising the country after the devastating 1992-95 war. Bosnia is hoping to start negotiations on an association and stabilisation agreement with the bloc this year.