Arsenal and Manchester United had scouts posted for Benfica's clash with VitoriaGuimaraes last weekend.
O Jogo says Arsenal had representatives in the stands to see Benfica winger Andrij Zivkovic and defender Reuben Dias.
United also had scouts checking the young duo as Benfica won 2-0 thanks to a brace from Jonas.
Dias, 20, has been a revelation for Benfica this season, breaking into the first team and now chasing a spot in Portugal's World Cup squad.
He only made his debut with Benfica in September.