Sir Alex Ferguson signed the player on the recommendation of former assistant Carlos Queiroz, but the winger has since struggled to make an impact since his move in 2010
Bebe, 21, is currently on loan at Turkish side Besiktas but signed for Sir Alex Ferguson's side in the summer of 2010 from Portuguese side Vitória on the recommendation of former assistant Carlos Queiroz, despite playing in just six pre-season friendlies for first division side Vitória.
Ferguson has since stated that he is the first and only player he has signed in a long managerial career without having watched him at least once first, even on video.
A spokesman for United said: "Clearly if the police ask us for information, we will co-operate with them. Nobody is suggesting that we have done anything wrong."
Police are thought to be investigating an anti-corruption charge made by the player's former agent, Gonçalo Reis, after it emerged that he was sacked by Bebe just two days prior to his big-money move to England.
The agent that brokered the transfer was Jorge Mendes, who also acts as agent to United stars Nani and Anderson as well as overseeing Cristiano Ronaldo and Jose Mourinho's deals.
Mendes was said to have been personally paid €3.6 million (£2.89m) of the €9m (£7.2m) transfer fee for his part in the deal, which comes to about 40% of the deal. He claims to own 30% of Bebe's 'economic rights' as part-ownership of the player, while 10% of the fee received comes as part of his commission, but only became an agent to Bebe days before his move to United.
The judicial police national unit for combating corruption, part of the Justice Ministry based in Lisbon, are responsible for the investigation. Reis, who has already been questioned, claims that he had an exclusive two-year contract with the player from August 2009 onwards. Mendes and his agency Gestifute have repeatedly denied poaching the player from Reis.