Newspaper Bild reported former City winger Sane was hit in the face by the Senegal attacker, suffering a cut lip after Tuesday's loss.
"The reason is misconduct by Mane after FC Bayern's Champions League game at Manchester City.
"In addition, Mane will receive a fine," they added.
Bayern declined requests to comment on the altercation.
Bild reported the clash started in the dying stages of Bayern's loss in Manchester, with footage showing the two arguing on the pitch.
Mane and Sane were seen on the training pitch early on Thursday.
The loss was Bayern's biggest Champions League defeat since 2017.
The six-time European champions now have little hope of turning over the deficit in next Wednesday's return leg in Munich to make it to the semi-finals.
Mane has endured a frustrating time since joining the German champions from Liverpool in the summer of 2022.
The two-time African Player of the Year scored six goals in his first seven matches in all competitions for Bayern, but has not scored since October.
Mane suffered a leg injury in November which kept him out of Senegal's Qatar World Cup campaign and saw him miss nine matches for Bayern.