Real Madrid's Uruguayan midfielder Federico Valverde was taken to the hospital with a cut head on Thursday after a reported dressing-room fight with Frenchman Aurelien Tchouameni.
Real later confirmed that team captain Valverde, who was subsequently discharged, sustained a head injury and will be sidelined for up to two weeks.
"Following tests carried out today on our player Fede Valverde by Real Madrid's medical team, he has been diagnosed with a head trauma," the club said in a statement.
"Valverde is at home and in good condition; he will need to rest for between 10 and 14 days, in line with medical protocols for this diagnosis."
The incident unfolded at the club's Valdebebas training ground the day after an earlier altercation between the pair, media reports said.
The club later on Thursday said disciplinary proceedings have been opened against both players.
"Real Madrid announces that, following the incidents that took place this morning during the first-team training session, it has decided to open disciplinary proceedings against our players Federico Valverde and Aurelien Tchouameni," a statement said.
"The club will announce the outcomes of both cases in due course, once the relevant internal procedures have been completed."
Valverde later posted a statement on social media apologizing to the club and its supporters but denied that things got out of hand with a teammate and said that during "an argument," he had "accidentally knocked over a table."
The gravity of the episode 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 teammate but insisted it was "a one-off incident of no significance that has been resolved."
Spanish media had 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 quarterfinal exit to Bayern Munich, Real trail La Liga leaders Barcelona by 11 points with four matches remaining. The sides meet at the Camp Nou on Sunday in an El Clasico that could seal the title for the Catalans.