United manager Jose Mourinho was squirted with water as he clashed with City goalkeeper Ederson.
The Manchester Evening News reports Mourinho approached the City dressing room to request they celebrate their 14th successive league victory in a more dignified manner before a shouting match erupted between the United manager and Ederson.
City's Brazilian goalkeeper responded by shouting in Portuguese and exchanged verbals with Mourinho as the row escalated. Mourinho then had water tossed at him.
It is understood City captain Vincent Kompany, withdrawn at half-time during the game, intervened to try to defuse the row. United sources have played down the severity of the clash.