The detective who led the police investigation into Adam Johnson's offending said his victim will "want to know why he was allowed back on the pitch."
Detective Inspector Aelfwynn Sampson, of Durham Police, said she spoke to Sunderland AFC on the day of his arrest.
She told BBC News: "They were given detail that he had met the girl and sexual activity had taken place."
The officer said SAFC was also told Johnson 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."