Gaston Ramirez is part of Middlesbrough's training squad in Spain as he attempts to rebuild his reputation on Teesside.
The Uruguay international handed in a transfer request last month with defending champions Leicester attempting to lure him away from the Riverside Stadium.
But Boro swiftly rejected the Foxes' approach and insisted the former Southampton midfielder, who has missed the last six games with a knee injury, was not for sale.
Head coach Aitor Karanka said Ramirez would not be leaving the club and included the 26-year-old in Middlesbrough's four-day warm-weather training break on the Costa Blanca.
"He is and he will be an important player in this team and he knows that," Karanka said. "He knows the effort that the club made to sign him last season and therefore that the club made this summer to sign him permanently."
Ramirez, who was given a few days off last week following Leicester's approach, has not made a senior appearance since the 0-0 Premier League draw with Leicester on January 2 and Boro have taken just two points from a possible 12 in his absence to slip to within a point of the relegation zone.
Karanka has been delighted with the player's contribution since his permanent capture during the summer following a successful loan spell, and is confident he can make an impact once again.
The pair were joined on the plane by full-back George Friend, who has missed the last two games with a calf injury sustained in the FA Cup fourth-round victory over Accrington Stanley.
Boro face in-form Everton at the Riverside on Saturday looking for a first league win since they beat Swansea 3-0 on December 17.