Boro first completed the signing of Uruguayan international Gaston Ramirez on loan from Southampton in the January 2016 transfer window.
Ramirez, who started his career in his home country with Penarol, played in Serie A with Bologna before joining Southampton in a £12m deal in the summer of 2012.
He scored eight goals in 55 appearances for the Saints and has featured 48 times for the club in the Premier League.
Ramirez was previously on loan at Hull City, where he made 22 Premier League appearances.
The player has a host of international experience, having played for Uruguay at Under-20 and Under-23 levels before going in to make 34 appearances for his country at senior level.
He featured in the 2014 World Cup and claimed an assist for Uruguay’s winning goal against Italy in the group stages.
A big hit during his initial loan spell, scoring 7 goals, Ramirez rejoined the club on a permanent basis in the summer of 2016.