Liverpool reportedly had scouts present as Porto played Lyon in the Europa League earlier this week.
During the January transfer window, the Merseyside giants secured a deal for Porto winger Luis Diaz, who has subsequently made a positive impact at Anfield.
While the Colombian winger had been a standout player for the Portuguese side, it has seemingly not stopped Liverpool returning to familiar territory.
According to O Jogo, Liverpool were among a number of clubs who were represented at Estadio do Dragao on Wednesday night.
Scouts would have witnessed Porto succumb to a 1-0 defeat at the hands of their French opponents, who had Lucas Paqueta to thank for a second-half goal.
Manchester United and Bayern Munich are also said to have been in attendance for the first leg of the last-16 tie.
