According to Marca, United hope placing a huge price on the 27-year-old, would discourage Real from trying to sign him.
De Gea reminded La Liga suitors just what he is capable of, with his wonder save against Sevilla in the Champions League on Wednesday night.
The Spanish goalkeeper was set to move to Real for £35m in the summer of 2015, only to see the move collapse in the final seconds of the window.
But if the move is going to happen again, it would cost Real €100m (£88m).
It is understood that De Gea’s value has come straight from the Glazer family, who will refuse to accept anything less.