Antonio Barragan has joined La Liga side Real Betis on a season-long loan.
The 30-year-old full-back, who arrived at Boro from Valencia last summer, returns to his native Spain in a loan arrangement.
Barragan has made 27 appearances with Boro, 26 of which were in the Premier League.
A string of injuries and absences along the Boro backline meant the former Liverpool, Deportivo La Coruna and Real Valladolid man made his club debut at centre-back in our opening-day fixture against Stoke City, while he was also occasionally deployed at left-back when needed.
But the majority of Barragan’s Boro appearances came in his customary right-back position, although he was himself subjected to a disrupted second half of the campaign owing to a troublesome hamstring injury.
Barragan's final match for the Teessiders last season was in April's 4-0 defeat to Bournemouth - he was replaced after just 23 minutes after Gaston Ramirez was shown a red card.