The forward left the pitch in tears during Monday's match, raising immediate fears over his fitness.
Medical tests reportedly point to a ruptured anterior cruciate ligament in his right knee, although the club is still awaiting a final medical report. Further examinations are scheduled before Samu undergoes surgery to confirm the full extent of the damage.
The injury is expected to sideline the striker for several months, with A Bola reports suggesting he is unlikely to return before the start of the 2026/27 season. That timeline would rule him out of the upcoming World Cup, dealing a major setback to both Porto and the Spanish national team.
According to the same source, the Spanish Football Federation has already been informed. Spain coach Luis de la Fuente now faces growing concerns in attack, particularly with doubts lingering over Mikel Merino's recovery, leaving his options increasingly limited ahead of the tournament.