Blackburn Rovers boss Gary Bowyer says it would take a substantial offer for anyone to sign Martin Olsson this summer.
Kilmarnock chairman Michael Johnston will resume discussions with Allan Johnston on Wednesday over the manager's position.
This season Tello has made 16 appearances in all competitions for Barca, having represented Spain at this summer's Olympics.
A Barcelona statement read: "Barcelona announce they have reached an agreement with the player Cristian Tello to extend his contract until June 30, 2016. His buy-out clause has been set at 10 million euros.
"The player will sign his contract on Monday, December 17, in the Barcelona offices."