Complex sentence: However, he is registered as a loan by Parma because FIFA does not allow a player to be in three teams in one football term; therefore, having been registered by Monterrey he would not had been able to play for Real Betis.
Split into simpler sentences: However, he is registered as a loan by Parma because FIFA does not allow a player to be registered to three teams in one season. Therefore, having been registered by Monterrey he would not have been able to play for Real Betis.