Escape clauses are becoming increasingly common in contract negotiations throughout Europe, but Adler raised eyebrows at Leverkusen when he insisted he would only accept their offer of new terms if it made provision for his lifelong ambition to play for Manchester United.
Easy option: United could take advantage of escape clause to sign goalkeeper Rene Adler
Bosses at the BayArena reluctantly agreed to insert a clause, allowing him to leave for Old Trafford, should United meet their valuation, and the 25-year old duly signed.
The asking price is believed to be close on £20million, but the prospect of an immediate, hassle-free release from a deal that runs until 2012 may appeal to United manager Sir Alex Ferguson, who is determined his side's new long-term number one will be in place in plenty of time for Van der Sar's retirement at the end of the season.
Ferguson may try and capitalise on Liverpool's troubles with a bid for Spain's Pepe Reina and has also scrutinised the claims of Schalke's Manuel Neuer and Atletico Madrid's David de Gea.
But Adler may yet force his way to the top of the shortlist after being capped nine times by Germany since making his international debut two years ago and making little secret of his longing to play for his boyhood idols.
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Managing director Wolfgang Holzhauser confirmed the clause tailored specifically to Adler's United ambitions, saying: 'It is an escape clause with a difference, because it only refers to one club. If United offer a certain amount, we have to let Rene go.
'He has always supported them, and he wanted to make sure the door was open, should they come calling. I know they have watched him quite a few times, so it may be difficult for us.'
Former Germany striker and manager Rudi Voller, now Leverkusen sporting director, admitted their plans to open talks on a new deal would have to go on hold.
'We would like to offer him another contract, because we want to keep him here,' he said. 'But we know what we are up against. If United follow up their interest, there is not much we can do.'
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