Herrera, 29, played for the Portuguese side for six seasons and has 70 international caps for Mexico.
Portuguese media reported that Herrera had not renewed his contract with Porto and that Atletico would pay only a nominal fee for him.
Atletico confirmed on Wednesday that Premier League champions Manchester City have paid the 70 million euro (£63 million) buyout clause to sign their Spanish international holding midfielder Rodri.
(Reporting by Joan Faus, editing by Ed Osmond)
