REAL MADRID have a buy-back clause in their transfer agreement with Arsenal for Mesut Oezil, according to leaked transfer documents.

A contract on the Football Leaks website shows that the London club must notify Real if they ever intend to sell the World Cup winner to another Spanish club.

The financial terms of the offer received for the Germany playmaker would be disclosed to Real, who would have 48 hours to decide whether to match the offer, or until noon, London time, on the final day of the relevant transfer window, whichever comes first.

Should a rival Spanish club sign Oezil for more than €50m, Real would be entitled to 33 per cent of the profit.

The contract shows Arsenal paid an initial fee of €44m when they signed Oezil in September 2013, with the fee rising to a maximum of €50m.

Six separate €1m payments, up to a maximum of €6m, 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, the contract states.

An Arsenal spokesman said: "We don't discuss contracts of any of our players."

Elsewhere, Eric Black is set to join Aston Villa's backroom staff.

The 52-year-old has left his role as Rotherham assistant manager and Press Association Sport understands he will take up a similar role under Remi Garde at Villa Park.

Villa are bottom of the Barclays Premier League and Garde has been working with assistant Reginald Ray and fitness coach Robert Duverne since replacing Tim Sherwood in November.

Black joined Rotherham as first-team coach last summer, being appointed as Neil Redfearn's number two in October.

He had a one-game spell as caretaker manager, losing 2-1 to Burnley in October, after Steve Evans' exit.

Black has also been assistant manager of Villa's rivals Birmingham City under Steve Bruce and worked with Bruce at Sunderland and Wigan.

He told Rotherham's official site: "I have really enjoyed working at Rotherham and I have met and worked with some terrific individuals.

"I didn't know Neil before he arrived but he was brilliant to me from day one. He is an exceptional coach, one of the best I have worked with, and with the support of the chairman and everyone else I am sure he will take the club forward."

Villa are 10 points from safety in the league and host Manchester City in the FA Cup on Saturday.

Meanwhile Ramires, the Chelsea midfielder, could soon leave Stamford Bridge with Chinese side Jiangsu Suning reportedly making a £25m move for the player.

The Brazil international, who joined from Benfica in 2010 for a reported £18m, only signed a new four-year contract, until June 2019, in October.