The trigger, according to Marca, is primarily physical. Mbappé has missed 10 matches and spent 53 days sidelined through five separate injuries since the turn of the year, beginning with a knee problem sustained against Celta Vigo in December.
The repeated absences have removed him from the daily rhythms of the group at the club's training base in Valdebebas, and that distance has taken on a larger significance as the season has wound down without trophies.
Off-field decisions have compounded the situation. A trip to Italy with his girlfriend while teammates prepared for Sunday's game at Espanyol drew attention internally, not because he was alone in travelling — other injured players had free days — but because his profile and the timing made it impossible to ignore. Real Madrid coach Álvaro Arbeloa addressed the trip carefully after the match.
"All planning regarding injured players is overseen by Real Madrid's medical staff, who determine when they need to come in and when they don't. From there, each player in their free time does what they consider appropriate — that's not something I can get into."
The response was notable for what it did not include. Arbeloa, who had previously shielded Mbappé in public, offered no defence of the player's choices this time. A brief, cold exchange between the two after Mbappé's substitution in the draw with Real Betis was observed by those present and taken as a further signal of the shift.
In the same period, Vinicius Junior has cemented himself as the undisputed leader of the group. He has carried Real Madrid through their most difficult run of the season, scoring a brace against Espanyol on Sunday to delay Barcelona's title celebrations, and Arbeloa has been fulsome in his praise of the Brazilian.
The contrast is pointed. The squad's unity with Vinicius is described as complete. With Mbappé, the picture is more complicated — even as he remains the club's top scorer this season with 41 goals.
The pair's personal relationship is understood to remain intact. The two were reported to have dined together with their partners in recent weeks. But the broader dynamic within the squad has shifted, and with El Clásico at Camp Nou on Sunday, it is Vinicius who arrives as Madrid's indisputable figurehead.