According to Bild, coach Pep Guardiola read the riot act prior to the top-of-the-table clash with Borussia Dortmund, which the European champion won 3-0.
"Whoever it is, heads will roll," he is quoted as saying. "I'm going to throw that person out and he will never play under me."
Rummenigge confirmed Guardiola's remarks during the team meeting and that they are searching for the source.
"Of course something like this is not to Pep Guardiola's liking," Rummenigge told Sky television.
"The coach is training behind closed doors at times for a reason and it's obvious that it's not something which pleases anybody.
"Somebody clearly thinks they're gaining an advantage through revealing information.
"We're not going to consult with the NSA (