The 18-year-old, who is 6ft 3in, represented Brescia and Atalanta BC during his youth career before making the move to Benfica in the summer of 2020.
Ndour is yet to make his first-team debut for his Portuguese club, but he has represented their B side on 40 occasions, contributing four goals and one assist in the process.
The midfielder has also played 22 times for Benfica Under-23s, but there is currently speculation surrounding his future with Benfica, as his contract is due to expire next June.
According to Tutto Salernitana, Man United are keeping a close eye on Ndour's development ahead of a potential move for him in 2023.
The report claims that the former Italy Under-18s international could be available fur a cut-price fee in January, as Benfica run the risk of losing him on a free transfer next summer.
As well as Man United, Paris Saint-Germain and Juventus are said to be showing an interest in the teenager.
Ndour is the youngest-ever debutant for Benfica B, having turned out for the team at the age of 16 years and 279 days, taking the record previously held by Atletico Madrid's Joao Felix.
There is currently widespread speculation surrounding another Benfica midfielder in the shape of Enzo Fernandez, with Man United also believed to be keen on the Argentina international.
Liverpool and Chelsea are also among the clubs to be linked with Fernandez, who played a key role in Argentina winning the 2022 World Cup.
Benfica released a statement on Thursday evening denying that club president Rui Costa had said that Fernandez could leave in January if his release clause, which is in excess of £100m, was met.
"SL Benfica clarifies that at no time did the President of the Club, Rui Costa, utter the words that are being circulated in Italy by DAZN," read a statement from the club.
"Sport Lisboa e Benfica reiterates its intention to count on the player Enzo Fernandez until the end of the season."
Man United will allegedly only be able to make loan signings during the January market due to their ownership situation, with the Glazers attempting to sell the club.
The 20-time English champions will be bidding to boost their top-four hopes in the Premier League when they travel to Wolverhampton Wanderers on Saturday afternoon.