His victim has asked why he was allowed to keep on playing.
Det Insp Aelfwynn Sampson from Durham Police, the lead investigator of the case, said she met Sunderland chief executive Margaret Byrne on 2 March 2015.
She told BBC News: “They were given detail that he had met the girl and sexual activity had taken place.”
She said the club was also told he had exchanged messages with the girl.
She added: “At the centre of this we have a 15-year-old girl who was an avid Sunderland fan and a massive fan of Adam Johnson, she describes him as her idol, she’ll want to know why he was allowed back on the pitch.”
Det Insp Sampson had told Adam Johnson’s trial she had met Ms Byrne to outline the case.
The Sunderland Echo reported the officer said particulars of the offences were not discussed as Johnson had not been interviewed.
Sunderland are yet to respond to the specific claim about the meeting with Durham Police.
Johnson was suspended for two weeks but then allowed to play again, with the club saying they understood he planned to deny all the charges against him.
The club sacked him on the first day of his trial after he admitted grooming and kissing the girl.
During his trial Johnson said Sunderland knew he had kissed the girl, but in a statement released after the verdicts the club “strongly refuted” any claim that they knew he planned to admit any of the charges.
The statement said: “It is understood that a suggestion was made that the club knew all along that Mr Johnson was intending to change his plea just before trial to enable him to continue to play football for the club and that the club may also have been involved in tactical discussions about the plea.
“This is utterly without foundation and is refuted in the strongest possible terms.
“The club never placed any pressure or demands on Mr Johnson to play football during this process.”