Mantato, 16, has scored six goals and registered one assist in nine appearances at academy level this season, including six goals in eight appearances in the Under-18s Premier League.
The Englishman has netted four times in his last three league outings, including a goal against Everton Under-18s last time out, and he is regarded as one of the best young talents in the youth system at the club.
According to the Manchester Evening News, Amorim has already been made aware of Mantato, who has drawn comparisons with Arsenal star Bukayo Saka due to his progression up the field.
Like Saka, Mantato was initially regarded as an attacking left-back, but he is now operating as a right-sided attacker, and it is believed that he could be given a chance as a wing-back by Amorim.
Amorim 'to keep an eye' on Man United youngster Mantato
It is believed that Amorim will look to implement a 3-4-3 system at Man United, having had huge success at Sporting Lisbon with that formation, and it could be on display when the Red Devils head to Ipswich Town in the Premier League on November 24.
Diogo Dalot and Noussair Mazraoui are currently the first-team options for the right-sided wing-back role, but it remains to be seen whether either are able to convince Amorim in the coming weeks.
Much will also depend on the fitness of Luke Shaw and Tyrell Malacia, as it is likely that Dalot or Mazraoui will be asked to play as the left-sided wing-back until the left-back duo are back to full fitness.
Shaw has returned to training, having overcome a calf problem, but the England international has not made a single appearance this season, and there remain concerns over his long-term fitness.
Malacia, meanwhile, played 45 minutes for Man United Under-21s earlier this week, but he has not played for the first team since the middle of 2023 due to a severe knee injury which is believed to have required two separate operations.
How is Obi Martin performing at Man United?
Man United have another huge talent in their academy system, with the club winning the race to sign Chido Obi Martin over the summer after the youngster decided against signing a new deal at Arsenal.
The 16-year-old has already made a big impression this season, scoring four times and registering one assist in four appearances for Man United Under-18s, and he will also undoubtedly be on Amorim's radar.
Obi Martin scored 32 goals in 18 appearances for Arsenal Under-18s during the 2023-24 campaign, including 28 goals in his final nine appearances of the season, while he famously scored 10 times for Arsenal Under-16s in a single match against Liverpool Under-16s last November.