The Colombia international has been in fine form since joining Porto from Jaguares at the start of the 2012-13 campaign, and his good performances have not gone unnoticed elsewhere.
"I can confirm that there's a strong interest from Barcelona. They are not the only Spanish team keeping tabs on him, though. There's an important team from Madrid as well," Fiore told Tuttomercatoweb."Additionally, there is serious interest from a big Italian team, and a few other clubs have inquired about his availability, too."
Fiore admitted that Porto won't sell Martinez on the cheap.
"Porto might study any offers they get, but we're talking about big bids here given the player's importance to the club."
The 26-year-old attacker's contract with Porto is due to expire in 2016.