At the European Championship of 1976 in Yugoslavia, Thomas was the referee of the semi-final between Czechoslovakia and the Netherlands. In the extra time of that match, he missed a rough foul by Antonín Panenka on Johan Cruyff, after which Zdenek Nehoda was able to score the decisive goal. Willem van Hanegem refused to play on after the incident and received a red card. In a 2008 documentary by the Dutch TV program Andere Tijden Sport, Thomas admitted he made a mistake by not noticing the foul.