That was after French defender Florian Lejeune joined from Eibar and Christian Atsu had made a permanent switch from Chelsea.
Reportedly undergoing a medical with the club yesterday, Merino could be inked to a loan to buy deal with Newcastle United before the weekend.
Spanish media outlet Marca is reporting that Newcastle United have swooped in and beaten the Basque club to the signature of the 21-year-old Spanish global. His father also played for the Spanish club.
The midfielder, who can also operate as a centre-half, was part of the Spanish u21 team that made it to the final of this summer's European Championships, before being beaten by Germany in the final.
Benitez plans to field him alongside Jonjo Shelvey in central midfield as he looks to stake his claim in the Premier league once more, having secured immediate promotion for the North East club last season. His dribbling is strong and he can comfortably bring the ball forward from a defensive position, something Rafa puts value in. Merino will provide a young, talented, versatile player ready to prove himself at the top level.