De Gea looks set to leave United this summer after rejecting a new contract at Old Trafford.
Real are keen to bring the player back to La Liga but will have to agree a fee with United unless they want to wait for his current deal to expire in a year's time.
And while a £30million fee has been mooted, United are interested in getting at least one player back in any deal, according to reports in Spain.
According to AS, United have asked about the availability of four Real stars.
It is claimed the Red Devils have asked about Gareth Bale, Cristiano Ronaldo, Karim Benzema and Raphael Varane.
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Benzema, Bale and Ronaldo are wanted by Manchester United
As keen as Real are to land De Gea, however, they have told United that none of the quartet are currently available as part of negotiations.
United raided Real for Angel Di Maria last summer but their hopes of landing another big-name player from the Spanish capital this summer appear to have hit a road-block.
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