Hoffenheim coach Ralf Rangnick has been asked to explain his claims that other Bundesliga clubs have flouted anti-doping rules after two of his players were late for a random test.
Christoph Janker and Andreas Ibertsberger both reported for their doping tests 10 minutes late after their team's 1-1 draw at Borussia Monchengladbach on February 7.
Although the results were negative, they still risk punishment for not sticking to strict rules which state that players must report for the doping test straight after the final whistle of the match and not return to the dressing room before.
Rangnick claimed they had only returned to change their shirts, causing a minor delay, but suggested it is common practice in the Bundesliga.
However, the German Football Association (DFB) are eager to find out exactly what the Hoffenheim coach means since they firmly refute their rules are being bent in any way.
"Without a doubt, the DFB strictly follows the anti-doping regulations," said the DFB's vice-president Dr. Rainer Koch.
"Should any incidents which have previously been unknown become known due to the comments of Mr Rangnick, then we will open up an investigation immediately."
Rangnick has therefore been asked to "back-up" the comments he made on SWR television.