The Su says United are understood to have approached Porto with a view to signing their attacking midfielder.
Moutinho, 25, would follow Cristiano Ronaldo and Nani on the successful track from Portugal to Old Trafford.
Spurs and Chelsea are also interested in the player, who this week praised Andre Villas-Boas.
AVB is set to take over at White Hart Lane and was Moutinho’s old boss at Porto. But, despite that, Moutinho still prefers the move to United.