Antonio Barragan signed a three-year contract with Boro during the summer of 2016.
The 29-year-old right-back joined from Valencia and made his first appearance for the club during the pre-season trip to Marbella.
The summer switch marked a return to England for the defender, who was first signed from Sevilla by Liverpool as an 18-year-old who had yet to play a first team game.
Barragan played just once for the Reds, and in doing so became the club's youngest ever foreign-born player to feature in a European tie, before he returned to Spain the following summer to join Deportivo La Coruna.
He moved to Valladolid two years later before joining Valencia in the summer of 2011, where he made over 150 appearances for the club.