Porto sign Mexican international Herrera
Herrera, a 23-year-old central midfielder, has agreed a four-year deal which includes a 40 million euros buyout clause.
He will strengthen Porto's midfield after Joao Moutinho and James Rodriguez were sold to Monaco for 70 million euros.
"I consider myself a dynamic and dedicated player, who is always moving and looking for the ball," Herrera told Porto's website.
"I like to show up in attacking areas and also know how to create goals."