The 21-year-old has been linked with several Premier League sides this season after impressing for Benfica.
Portuguese radio station TSF says Benfica president Luis Filipe Vieira has rejected a bid from United that was in the region of €10million, with out-of-favour winger Nani also offered in exchange.
Di Maria has a €40million release clause in his contract, but it is believed Benfica are ready to sell for around €30million.
