It was revealed back in January 2016 by Football Leaks (via the Guardian) that Real Madrid have first refusal on signing Ozil if he ever leaves the Emirates. In addition, a so called “Anti-Barca” clause was inserted which means Real would be entitled to 33% of any transfer fee above €50m if the German international is sold to another Spanish club.
The fact is though these clauses will not really mean anything if Ozil opts to sign for Barcelona on a free transfer next summer. Don Balon report that Barca are keen to have a controlling presence in central midfield, which Andres Iniesta currently only provides them.
Earlier this month, Arsenal manager Arsene Wenger revealed that contract talks with Ozil have not broken down, but had just slowed down due to the start of the Premier League season. The midfielder is just over three months away from being able to speak to other clubs about leaving on a free transfer in July.