Federico Valverde went to hospital with a head injury after a dressing room row with Real Madrid team-mate Aurelien Tchouameni but denied the pair “came to blows”.
The Uruguayan said the injury, which will keep him out of Sunday’s match against Barcelona, was caused when he “accidentally hit a table”.
Midfielder Valverde explained he suffered a “small cut on my forehead that required a routine visit to the hospital” during what he described as an argument.
The club, who have opened disciplinary proceedings against both players, said Valverde, 27, has been diagnosed with a cranioencephalic trauma, a type of concussion.
The Thursday morning incident came just three days before Real face a crunch title match against rivals – and likely champions – Barcelona.
“Valverde is at home in good condition and will have to remain at rest for 10 to 14 days, as indicated by the medical protocols for this diagnosis,” the club said.
In a statement on Instagram, Valverde said: “At no point did my team-mate hit me, and I didn’t hit him either, although I understand it’s easier for you to believe we came to blows or that it was intentional, but that didn’t happen.
“I feel that my anger about the situation, my frustration at seeing some of us struggling to get through the end of the season on our last legs, giving it our all, pushed me to the point of arguing with a team-mate.
“I’m sorry. I’m truly sorry because this situation hurts me, this moment we’re going through is painful. Real Madrid is one of the most important things in my life, and I can’t just turn a blind eye to it.
“The result is a build-up of things that culminate in a senseless fight, damaging my image and leaving room for doubt – for people to fabricate stories, slander me, and sensationalise an incident.
“I have no doubt that any disagreements we might have off the field ceases to exist on it, and if I have to defend the team inside a stadium, I’ll be the first to do so.”
Valverde also confirmed widespread reports that the pair had another row on Wednesday, adding: “In a normal locker room, these things can happen and are usually resolved internally without it becoming public knowledge.
“Clearly, someone here is spreading rumours, and with a season without titles, where Real Madrid is always under scrutiny, everything gets blown out of proportion.”
An emergency meeting was called for Thursday evening with Real president Florentino Perez and his staff, plus head coach Alvaro Arbeloa and club captain Dani Carvajal.
Real have have had disappointing season, sitting 11 points behind Barcelona in La Liga with four games to go, while they also exited the Champions League at the quarter-final stage with Valverde describing it as another “wasted year”.
Anything other than a win for Real in Sunday’s El Clasico at the Nou Camp will hand Barcelona a second consecutive La Liga title, with three games to spare.
A spat between team-mates in the run-up to the game added to Real’s difficulties.
In their statement about the altercation between Valverde and Tchouameni, Real added: “The club will provide updates on the resolutions of both proceedings once the corresponding internal procedures have been completed.”
Spanish media say the incident has been described internally by several members of staff as “the most serious ever experienced in Valdebebas”.