Manchester United scouts saw Porto ace Luis Diaz score in victory over Famalicao on Sunday.
O Jogo says Diaz has scored 16 goals and provided six assists in 28 appearances this campaign to help Porto to top spot in Primeira Liga, where they have a six-point lead over Sporting Lisbon.
That form has attracted interest from some of Europe's leading clubs and United were among a trio of clubs watching him in action on Sunday.
It's claimed Atletico Madrid and Borussia Dortmund also had scouts in attendance to watch Diaz, who scored Porto's second goal of the game in the 3-1 victory over Famalicao.
Diaz produced a composed finish to curl home into the far corner and being set free by a sublime through ball from midfielder Otavio.
It's been reported that Diaz has a £67million release clause and any club wishing to land him would need to pay it because he still has two and a half years left on his current deal.
Need a VPN? Or seeking to switch? Then support Tribal Football by clicking here to sign up with our official partners NordVPN. Not only will you receive the best VPN experience, but also great discounts by signing up via Tribal Football. Thanks for your support!