Manchester United reportedly sent scouts to watch Benfica defender Ruben Dias in action during his team's 1-0 defeat to Dinamo Zagreb in the first leg of their Europa League last-16 clash on Thursday night.
Dias, 21, came through the youth system at Benfica and has gone on to make 72 first-team appearances.
United are widely expected to spend big on a new centre-back this summer, and according to The Sun, the 20-time English champions closely watched Dias's performance against Dinamo Zagreb last week.
Dias, who has captained Benfica this season, has a contract in Portugal until the summer of 2023.
Earlier this month, it was reported that United were prepared to spend £155m to bring both Dias and Felix to Old Trafford in this summer's transfer window.