Real Madrid have a buy-back clause for Arsenal midfielder Mesut Ozil that prevents the German World Cup winner from being sold to another Spanish club without Los Blancos’ consent, according to leaked transfer documents on the Football Leaks website.

According to the leaked documents, Arsenal must notify Real Madrid if they ever intend to sell Ozil to another Spanish club. The financial details of any such deal would be disclosed to Real, who would then have 48 hours or until noon, London time, on the final day of the relevant transfer window, whichever comes first, to decide whether to match the offer of the buying Spanish club.

The contract, which appeared on the whistle blowing website, states Real Madrid would be entitled to 33% of the profit should Arsenal sell Ozil to a Spanish club for more than €50m. It also shows Arsenal paid €44m to buy Ozil from Real in September 2013, with the fee rising to a maximum of €50m.

The extra €6m comes from six separate €1m payments, which are contingent on Arsenal qualifying for the Champions League group stages in any season from July 2014 onwards. Each one must be paid within 30 days of qualification being secured, according to the contract.

The revelations come days after the financial details of Gareth Bale’s move to Real Madrid were disclosed, which cleared the air on who is the most expensive footballer ever. Following the latest leaks, an Arsenal spokesman said: “We don’t discuss contracts of any of our players.”