Manchester United sent scouts to Benfica’s 1-1 draw with Vitoria Setubal on Sunday with Victor Lindelof in action for the Eagles.
The Swedish defender was linked with a move to Old Trafford last season and shares the same agent as Reds boss Jose Mourinho – Jorge Mendes.
Lindelof, 22, had an excellent season with Benfica last time around but did not enjoy the best of summers with his national team at Euro 2016.
Chelsea and Inter have both recently been linked to the centre-back but neither of those clubs were represented at the Stadium of Light where the other big clubs present were Arsenal, Tottenham, Atletico Madrid and Sevilla.
Lindelof is under contract with Benfica until 2020 and is reportedly worth between £12-15million.