Madrid are competing with Barcelona for the signature of the Brazil international, who wants to return to La Liga before Europe's transfer window closes next Monday.
PSG want to recoup the £198m they paid to sign Neymar from Barcelona in 2017, but neither the Blaugrana nor Madrid can afford to pay that fee outright.
Both clubs are therefore looking for alternative ways to fund a deal, with Madrid reportedly keen to bring the price down by offering to send some of their fringe players to the Parc des Prince.
And PSG have now told los Blancos that they want Vinicius Junior and will reject any proposal that does not include him as a makeweight.
Madrid do not want to lose the 19-year-old Brazilian but could be forced into a rethink if they want to sign Neymar this summer.
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