Inter striker Romelu Lukaku is reported to have got into it with midfielder Marcelo Brozovic following his side's Champions League draw with Slavia Prague, with only Alexis Sanchez preventing the argument from getting physical.
Only a stoppage time strike from substitute Nicolo Barella saved the Serie A leaders from Champions League humiliation on Tuesday, as the Serbians had led since the 62nd minute after Peter Olayinka's opener.
Antonio Conte's men may have salvaged a point from their opening group game but they were a long way from content, and reports soon emerged of an incident in the dressing room involving the duo.
Though their conversation was initially calm, things escalated when the Croatian turned the blame on Lukaku, pointing to a missed opportunity to open the scoring before disaster had struck through the visitors' opener.
Heated words were exchanged before the two came face to face, with Sanchez then stepping in to prevent the dispute from coming to blows.
Such is the serious nature of the incident that manager Conte is believed to have been furious in the wake of it, and has already asked chairman Beppe Marotta to 'deal with' the situation behind closed doors.
It may mean a fine for one or both men, while there is also a suggestion that Brozovic could be dropped, with Conte nervous about upsetting his £73m signing by keeping him in the team.
Inter face Milan in the first derby of the season at San Siro on Saturday evening, and a win would go a long way towards settling any underlying tensions that may exist.