The 21-year-old forward's £7.5m move from Vitoria Guimaraes to Old Trafford is being probed by Portuguese police following reports that a large sum of money is unaccounted for
A reported £3m has gone missing from the transfer fee which was negotiated between Portuguese side Vitoria Guimaraes and United in August 2010.
It was claimed by directors of Vitoria Guimaraes that a sum of around €3m went to Bebe's agent as part of the dealings between to the two clubs, although the agent's company would neither confirm nor deny that the police had contacted them.
There is, however no suggestion that United have done anything wrong in the transfer process, and the club have gone on record as saying none of the fee went directly to an agent.
The transfer came as a shock to many at the time, as United boss Sir Alex Ferguson admitted he had not actually seen Bebe play, but had signed him on the recommendation of his former assistant, Carlos Queiroz.
The United player is currently on loan to Turkish side Besiktas, having failed to make an impact at Old Trafford. He made only three starts last season, none of which were in the Premier League.
Bebe is expected to be sold by United in the summer, with reports suggesting that he may return to Portugal.