Club concerned they have overpaid by almost £1million for Masuaku

West Ham United have launched an investigation into the £6.2million deal that saw Arthur Masuaku move to the club from Greek champions Olympiacos in the summer.

Senior club officials are concerned they have overpaid by almost £1m for the 22-year-old French left back and sent a representative to Athens last week to establish if that is the case.

West Ham are trying to ascertain whether someone has been paid who was not declared on the official transfer document.

West Ham defender Arthur Masuaku (right) in action against Watford last Saturday

The 22-year-old moved to east London from Olympiacos in a £6.2million deal in the summer

With a mandate from chairman David Sullivan and club secretary Andrew Pincher, the investigator was charged with trying to identify who received commission for the deal as there is a fear Masuaku’s price was inflated.

It is believed the club hierarchy want to satisfy themselves that the transfer business was conducted properly at both ends of the deal.

Greek football is in chaos with the domestic championship delayed as the government tries to tackle alleged corruption. Olympiacos chairman Vangelis Marinakis is also under investigation as part of a match-fixing probe.

West Ham confirmed to Sportsmail on Monday night that they are undertaking an investigation.

West Ham chairman David Sullivan has given an investigator a mandate to investigate the deal