The Daily Mail reports that United held talks in London on Friday over the signing of the 18-year-old midfielder.
United are hoping to complete the signing of the talented midfielder in January in a move to avoid a summer bidding war.
Sanches has a buy-out clause in his contract of nearly £60million, but Benfica are expected to sell for around half that sum, with add-ons.
United could sign Sanches in a deal that would see him stay on loan at Benfica for the rest of this season.
