Manchester City are not concerned by a Fifa investigation into the £42m transfer of Eliaquim Mangala from Porto, according to reports.

The world football governing body is set to examine whether investment company Doyen Sports improperly aided in the negotiation of the deal.

Only around 57 per cent of Mangala's Porto contract was owned by the club, with the remainder shared between Doyen and fellow investors Robi Plus.

The investigation, orginally reported by Bloomberg, centres on the allegation that Porto allowed Doyen to negotiate the sale of their stake on the club's behalf.

Any such delegation would contravene Fifa rules. If found guilty, Porto could face a fine or transfer ban.

However, Manchester City sources have told ESPN they are confident that the transfer fee was paid in full to the Portuguese club rather than an agency and that they purchased 100 per cent of the player's contract.

Doyen Sports are an investment company who speculate on the futures of promising footballers. The group have a history of third-party ownership in Portugal, where the practice of investing in players contracts is permitted and widely practiced.

The company part-owned Manchester United defender Marcos Rojo before he moved to the club from Sporting Lisbon, as well as Chelsea striker Falcao during his time at Porto.

Mangala's move to the Etihad Stadium made him the second most expensive defender in football history and the most expensive in Premier League outright.