Bayern Munich could be in trouble after having 12 players on the pitch for 17 seconds of their win over Freiburg.
The fourth official showed the wrong number on the board which meant Kingsley Coman did not know he was meant to come off in a late change.
Freiburg alerted the officials and there was a long delay and lots of confusion while it was sorted.
Bayern, who are seeking a 10th title in a row, are nine points above Borussia Dortmund with six games left.
However league rules say it is possible this victory could be overturned.
Referee Christian Dingert said it was “totally confused situation [and] now the DFB [German Football Association] must decide.”
Niklas Sule and Marcel Sabitzer both came on in the 86th minute, but only Corentin Tolisso came off.
“We drew the referee’s attention to the fact that Bayern had 11 outfield players on the pitch,” Freiburg director Jochen Saier told Sky.
It is thought they would need to lodge a formal complaint for Bayern to be punished.
Freiburg coach Christian Streich said: “I expect that we will not have to appeal anything. We abide by these rules and that is all I will say about it.”
Bayern boss Julian Nagelsmann said: “The fourth official showed the wrong number and Kingsley Coman didn’t know he had to go off. Mistakes happen.
“From the point of fair sport, there was nothing that speaks against it having been a fair game.”
Leon Goretzka’s goal was his first since 6 November, also against Freiburg
Leon Goretzka scored on his comeback from four months out with a knee injury for the opening goal when he headed in from Joshua Kimmich’s free-kick.
Nils Petersen levelled seconds after coming on with a first-time finish.
Substitute Serge Gnabry put Bayern ahead again with a good first touch and finish. Coman then drove in from the edge of the box before Sabitzer’s injury-time fourth.
Second-placed Dortmund lost 4-1 at home to RB Leipzig, with Konrad Laimer scoring twice and Christopher Nkunku and Dani Olmo also netting. Donyell Malen scored for Dortmund. (BBC Sports)
