Manchester United sent scouts to watch Benfica forward Joao Felix score twice against Maritimo on Monday.
The 19-year-old has emerged as one of the most exciting players on the summer market with Juventus and Manchester City also taking a keen interest despite his reputed £104million buy out clause.
United have monitored his progress for over a year but he has shown a marked maturity in his performances in recent months and scored 16 goals in the process.
United's regular Portuguese scout Joao Ferreira was in attendance as usual on Monday but was joined for a second opinion by one of United's lead scouts Simon Wells who is well regarded by the club's hierarchy. Felix scored two as Benfica won 6-0.
Juventus have already held talks with the teenager's representative Jorge Mendes while Manchester City have made initial enquiries after watching him again in recent weeks, notably as he scored a hat-trick for Benfica against Eintracht Frankfurt in the Europa League.
United want a dynamic and pacy forward who can play wide or centrally. They had considered Chelsea's Callum Hudson-Odoi but know the Stamford Bridge club are reluctant to sell and are intent on agreeing a new contract with the 18-year-old despite him being ruled out for up to four months with an Achilles injury suffered on Monday.
Borussia Dortmund have no intention of selling Jadon Sancho, another discussed, so United are assessing alternatives.
Benfica's asking price remains prohibitive but there is a belief among Europe's elite that a deal at a lower price with add-ons could be struck.
United also want a right-back and two midfielders and could add more if any significant players depart.