Leganes general director Martin Ortega has complained that Barcelona's acquisition of Denmark centre-forward Martin Braithwaite is "unfair" and damaging to the club.
Barcelona were granted permission to complete an emergency signing outside of the transfer window by the Royal Spanish Football Federation (RFEF), with Ousmane Dembele set for six months on the sidelines after undergoing surgery on a torn hamstring.
The Blaugrana were only able to target players from Spain or free agents during a 15-day period, with the likes of Inaki Williams, Angel Rodriguez, Roger Marti and Lucas Perez all linked with moves to Camp Nou.