William Carvalho
Carvalho scouted by both Arsenal and United. (Reuters) Reuters

Manchester United manager David Moyes has again sent scouts to the Alvalade Stadium to watch Sporting Lisbon midfielder William Carvalho, reports in Portugal claim.

The 21-year-old has garnered a reputation as one of the most prolific box-to-box midfielders in Europe, earning comparisons with French legend Patrick Vieira.

Arsenal boss Arsene Wenger has been monitoring him for several months while, according to Portuguese newspaper A Bola, Manchester United's scouts have also been to Portugal at least 12 times during this campaign, monitoring his amazing development.

Some reports claimed that the Premier League champions tried to convince Sporting to sell their star during the January transfer window, by offering Nani as part of the deal, but the Portuguese giants rejected the approach as they were not keen on selling a pivotal player in mid-season.

With Barcelona and Real Madrid also linked with Carvalho recently, it is understood that the youngster will be tempted to move to a bigger club over the summer and Manchester United and Arsenal are also ready to fight to secure his services.

Nevertheless, it is not going to be a cheap deal, as Carvalho's contract with his current club expires in 2018 and his release clause is £37.5m.

The defensive midfielder was named the best player in the Primera Liga by supporters during October and November, and after earning two caps with Portugal he hopes to make the trip to Brazil next summer.

Despite signing Juan Mata last January, Moyes is reportedly keen on making a number of new additions in the next transfer window and with Michael Carrick, Tom Cleverley and summer signing Marouane Fellaini failing to impress him this season the boss is especially concerned about bolstering his midfield.