The 21-year-old signed a new four-year contract in December last year, having played his way into the first-team reckoning at the Nou Camp.
However, following speculation linking Tello with the likes of Liverpool and Tottenham in the off-season, the Blaugrana have moved to increase his release clause to €25 million.
Tello's new deal will keep him contracted to the club until the end of the 2017/18 season.
The Sabadell-born player, who has represented Spain at various youth levels, made 34 appearances in all competitions last season, scoring eight goals in the process.
He is expected to provide cover for new signing Neymar in the upcoming La Liga campaign.