Real Madrid facing potential Osasuna lawsuit in La Liga opener if Franco Mastantuono plays

Real Madrid are set to kick off the 2025-26 La Liga season at the revamped Santiago Bernabeu against Osasuna. But the spotlight has shifted to new signing Franco Mastantuono, whose potential inclusion could trigger legal action from the visiting club.

After shining at River Plate and becoming the youngest player to debut for Argentina’s national team, Mastantuono arrived in Madrid this summer in a $60 million transfer. With Xabi Alonso instrumental in convincing him to join, the 18-year-old is seen as one of the breakout players to watch this season.

However, his participation in the La Liga opener may be in jeopardy due to questions over registration rules. According to Miguel Galán on El Chiringuito, Mastantuono is officially listed with Real Madrid Castilla, the club’s B team, in an apparent attempt to work around regulations on player registration for the first team.

Osasuna have already pursued similar action in the past, having filed a complaint against Barcelona last season for allegedly fielding Iñigo Martinez improperly. Reports suggest the club could take the same step against Real Madrid, accusing them of acting in “bad faith” by registering Mastantuono through alternative channels.

Under article 248 of the General Regulations of the Royal Spanish Football Federation, strict rules govern player eligibility. Ultimately, it will come down to how the authorities interpret the case. If Osasuna wish to act, they would have 24 hours after the match to file a complaint—after that, the window closes.

Xabi Alonso sets the stage for Mastantuono’s debut

Inside the club, there appears to be little concern about the possibility of sanctions. Alonso has already hinted he plans to give Mastantuono minutes. Ahead of Tuesday’s clash, the coach spoke glowingly about the Argentine teenager’s qualities.

“Yes, he could get minutes tomorrow,” Alonso said at Monday’s press conference. “He’s going to bring quality, energy. He’s committed defensively, he’s got good drive. In a short time I’ve seen that grit, that Argentine warrior spirit, but also real quality… he’s combative. And he’s got a spectacular left foot.”

Alonso also explained the situations where Mastantuono could make an impact. “Whether on set pieces, the final pass, or finishing, he’s very sharp. He’s young, but very mature for his age. We need to support him, but he’s already at a very high level,” the manager added.