On 15 September last year, Markus Zahn left his bright orange McLaren Spider in a car park bordering a paddock in Vogelsberg, a district in Hesse state.
A donkey called Vitus then chomped on the back of his car, he said. The court found Vitus's owners liable for €5800 of paintwork damage.
Police said Vitus may have confused the car with a carrot.
The donkey's owners could still appeal.
The owners argued that Vitus may not have been the culprit and that Mr Zahn should not have parked his car - reportedly worth €310,000 - next to the paddock.