The 28-year-old midfielder has been linked to a number of European clubs including Arsenal in recent times, with his contract at Porto set to expire at the end of the season.
He will be free to move to any club for nothing at the end of the season and the prospect of having such a talented midfielder for nothing has attracted a number of clubs as they begin plans to land him.
The Gunners have been linked with him for over a year, and was most recently said to be identified as a replacement for Aaron Ramsey.
The Welshman is also set to leave the Emirates on a free transfer at the end of the season after the club withdrew their contract renewal offer.
However, Arsenal now face competitions from Italy, with Roma and Inter both interested in landing Herrera on a free also.
Arsenal could do well to reach an early January agreement for the star midfielder ahead of a summer move to fend off rivals for his signature.
The Gunners are letting Ramsey go because he doesn’t fit into the club’s financial budget due to his excessive wage demands.