Bayer Leverkusen are confident that Hakan Calhanoglu will be a central figure at the club for many years.
Notts County have taken former Birmingham striker Akwasi Asante on trial after he turned down a move to Shrewsbury.
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."