Eliaquim Mangala joined Machester City from Porto in the summer of 2014 but FIFA are set to look into the transfer deal as the negotiations are believed to have defaulted in some rules.
The primary club being investigated are Porto as it is believed that Porto breached third party ownership rules when Mangala was sold to Manchester City. The premier league forbids the involvement of third party ownership in transfers and Manchester City seemingly have little to lose in the investigations as they are seemingly innocent and have no involvement.
FIFA are reported to be set to put the entire transaction under scrutiny and Porto might suffer sanctions if found guilty. Mangala and Manchester City however were not indicted in preliminary reports.