Chelsea and La Liga giants Real Madrid are also understood to be interested in the 21-year-old Angolan-born player.
Carvalho has a £37.5million buy-out clause in his contract and still has four years left on his deal, but David Moyes is a known admirer.
However, despite the interest, Carvalho says he is completely focused on doing well for the Portuguese club until the end of the season when he will make a decision regarding his future.
Speaking after Sporting's 2-1 win over Braga, Carvalho told journalists: "It's nice being praised and to know there are some big clubs interested in me."
And asked about his future, he added: "It could be Manchester United or Real Madrid. It's just nice to have a great European club after me, but at the moment I'm just totally focused on Sporting and doing my best until the end of the season.
"At the end of the campaign, we will see what happens."