Real Madrid's simmering tensions spilled over on Thursday when Federico Valverde and Frenchman Aurelien Tchouameni were involved in a dressing-room fight that left the Uruguayan in hospital with a deep cut to the head, several club sources said.
The incident unfolded at the club's Valdebebas training ground the day after an earlier altercation between the pair.
A Real Madrid spokesperson told Reuters he would not comment on what happens inside the changing room but that the club is still considering how to respond to the incident.
The sources said disciplinary proceedings have been opened against both players and could result in financial penalties or suspension.
The gravity of the episode also prompted an emergency meeting attended by senior club officials, with no players leaving the training ground for over an hour.
The aim was to try to halt an escalation of tensions that has left nerves frayed and the squad divided at a sensitive moment for the team.
The unrest follows another flashpoint earlier this week when defender Alvaro Carreras acknowledged he had been involved in a heated argument with a team mate but insisted it was "a one-off incident of no significance that has been resolved" after Spanish media reported an alleged incident between him and the club's German defender Antonio Ruediger.
Madrid's season has unravelled on multiple fronts. Manager Xabi Alonso was sacked midway through the campaign and his successor Alvaro Arbeloa has been unable to prevent the team sliding towards a second successive year without a trophy.
Following a Champions League quarter-final exit to Bayern Munich, Real trail LaLiga leaders Barcelona by 11 points with four matches remaining.
The sides meet at the Camp Nou on Sunday in a Clasico that could seal the title for the Catalans.
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