Bayern Munich have been told to reduce their unrealistic valuation of Franck Ribery or risk losing him for as little as £14million next summer.
The German club have repeatedly tried to scare off Chelsea, Manchester United, Real Madrid and Barcelona since the end of the season by valuing their 26-year-old star player as high as £70m.
But players' union FIFPro have threatened to report Bayern to the European Union if they are not prepared listen to serious offers next summer.
At that point, Ribery would be able to invoke little-used FIFA rule Article 17 to walk away from his current contract and have the compensation fee set in court.
The precendent was set to secure Andy Webster's transfer from Hearts to Wigan in 2006 when he unilaterally quit the Scottish club three-quarters of the way through a four-year contract.
After a long legal process, the fee was eventually set at £150,000. A similar case in 2007 saw Brazilian midfielder Matuzalem leave Shakhtar Donetsk for Real Zaragoza in 2007.
The Ukrainians demanded about £22m, but received less than half when the case went to the Court of Abitration for Sport.
The leading sport lawyer who worked on both cases, Juan de Dios Crespo, believes that if Ribery uses Article 17 next summer the fee will be between £13.9m and £19.1m.
Bayern are relaxed about the threats as it is understood that the G-14 group of elite European clubs had a gentlemen's aggreement not to use Article 17 to sign players from each other.
However, the G-14 was disbanded in February 2008 to be replaced by the UEFA-endorsed European Club Association, leaving a grey area as to whether the agreement is still valid.
In any case, Chelsea, who have strongly pursued attacking midfielder Ribery this summer, were never part of the G-14 and not party to any historic agreement on Article 17.
While Bayern's directors have consistently insisted Ribery is not for sale, new head coach Louis van Gaal is more philosophical about the chances of holding on to the former Marseille player.
'Franck has an important role in this team,' said Van Gaal, 'but in football you never know what is going to happen. Look at Cristiano Ronaldo.'