Celtic defender Virgil van Dijk insists he never asked to leave the club in the summer, and is happy where he is.
Roberto Martinez is not surprised by the interest shown in James McCarthy but is determined to keep him at Everton.
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."