West Ham are tracking Benfica striker Raul Jiminez.
O Jogo says West Ham had a scout in the stands for Porto's 1-0 win at Benfica.
A host of Premier League clubs had representatives looking at targets in Sunday's top-of-the-table Primeira Liga clash.
Manchester United, Everton, Leicester, Liverpool, West Ham, Tottenham, Aston Villa, Southampton and Swansea all had scouts at the game.
Benfica full-back Andre Almeida was apparently being watched by Leicester, with Everton taking notes on Porto striker Moussa Marega.
Spurs were said to have been scouting Porto's Ricardo Pereira during the clash.
Hector Herrera's strike won the game in the 90th minute as Porto hurdled Benfica to move two points clear at the top of the table.