The 21-year-old joined the Red Devils from Vitoria Guimaraes for a reported fee of £7.4m.
However, Portugese police are investigating claims from Vitoria that £3m of that transfer money was paid to the player's agent Jorges Mendes.
United, though, believe that there is no need for them to become involved.
"There is no need to comment at this stage because no one is alleging any wrongdoing by us," a United spokesman said.
Bebe is currently on loan at Turkish side Besiktas.