The Colombian has been in scintillating form this season, and has already seen his name linked with top European clubs.
El Mundo Deportivo claims that Barcelona have also joined the race, as the Catalans watched the player in Porto’s 5-0 win over Maritimo at the weekend.
Martinez largely impressed the visiting scouts by scoring a brace and taking his tally to eight goals in as many league games.
The 26-year-old joined Porto in an €8.8 million deal from Mexican side Jaguares in the summer, but has already starting to pay off the hefty transfer fee.
Besides scoring eight league goals, the highly-rated striker netted twice in team’s Champions League campaign.
Martinez has a long-term contract with the Dragons, with €40 million release clause inserted in his deal.