The Portuguese giants have reluctantly accepted they will struggle to keep him come the end of the season, and are believed to have identified a suitable replacement.
Carvalho is believed to have a £37.5million buy out clause in his contract, and Sporting have signalled they are ready to cash in by lining up Goncalo from neighbours Estoril.
Sporting believe they can land Goncalo for as little as £410,000, so are set to make a massive profit should Carvalho complete his move to Old Trafford.
David Moyes remains desperate to strengthen his struggling midfield, and has sent scouts to watch Carvalho in action at least eight times.
The most recent scouting trip came at the start of the month, when Moyes had Carvalho studied during Sporting’s 0-0 draw with Academica.
United would not be willing to pay the hefty release clause however, and would be looking to negotiate a cheaper deal, despite the fact Carvalho still has four years left to run on his current contract.
Sporting are set to play hardball, especially since Barcelona and Real Madrid are also rumoured to be interested in the 21-year-old midfielder.