The new deal will keep Mejias with the Riverside club until the summer of 2018.
Mejias joined Boro from Spanish giants Real Madrid in July 2014 and his previous deal was set to expire at the end of the season.
The new deal will keep Mejias with the Riverside club until the summer of 2018.
Mejias joined Boro from Spanish giants Real Madrid in July 2014 and his previous deal was set to expire at the end of the season.
