Red Devils boss Jose Mourinho is desperate to bolster his midfielder this summer and has identified Kroos as his number one target.
The German has been incredibly consistent for Los Blancos since joining from Bayern Munich in 2014.
And the Spanish giants are willing to negotiate a deal with United, but The Independent claim that De Gea must be included.
Real have not relinquished their interest in De Gea since they failed to sign him at the transfer deadline in 2015.
But now with considerable leverage, Real president Florentino Perez is hopeful he can finally sign the goalkeeper he has long desired.
The 27-year-old was believed to be close to signing a new contact with United, but contradicting reports have suggested that negotiations have yet to begun.