The 23-year-old has long been a target for City, with the France international viewed as the ideal player to slot in alongside captain Vincent Kompany at the heart of the defence.
The club attempted to sign Mangala during the January transfer window but were unable to agree terms with the player.
But reports in Portugal suggest Mangala, who was part of France's squad for the World Cup in Brazil, is now poised to head to Manchester for his medical.
Mangala began his career with Standard Liege in 2008, before joining Porto in 2011 where he has won two league titles.
City have already signed midfielder Fernando from Porto this summer, while Malaga goalkeeper Willy Caballero and Arsenal full-back Bacary Sagna have also been added to Manuel Pellegrini's options.