Manchester City's board are to launch an investigation into allegations chief executive Garry Cook sent an offensive email to the mother and agent of defender Nedum Onuoha.
A club statement read: "Following allegations made to the football club by Dr Anthonia Onuoha, subsequently reported in today's media, the Club can confirm that a board led review has been launched into the matter."
Dr Onuoha emailed City's football administrator, Brian Marwood, last October stating that, despite being "ravaged with cancer", she would continue to hold talks regarding a dispute over her son's contract.
A fortnight later, Dr Anthonia Onuoha alleges she received an email, seemingly from Cook addressed to Marwood, that said: "Ravaged with it!!......I don't now how you sleep at night. You used to be such a nice man when I worked with you at nike (sic)."
Dr Anthonia Onuoha replied the following day, writing: "Thanks very much for your insightful e-mail." Cook has since denied sending the email, citing that his account had been hacked while he was on holiday in South Africa.
Cook, who apologised for "any hurt or embarrassment this may have caused", told Dr Anthonia: "I cannot and will not condone this unacceptable behaviour. I can confirm Brian did not receive this e-mail and disciplinary action is currently underway regarding one of our employees."
Dr Anthonia Onuoha, though, has told the Sun: "When Cook replied to me, he said that he was confused, that he'd been away on holiday in South Africa and that somebody had hacked into his email account and whoever sent the email to Brian Marwood meant it as a practical joke. It was all very stressful at the time, in fact it still is.
"The illness I have is very stressful, I'm having chemotherapy and radiotherapy, including having radiotherapy on my brain and this year has been traumatic. I didn't want anybody adding to my stress but that is what they've done.
"The feeling of humiliation still persists. Now I just want the FA and the Premier League to see what's happened and to take the appropriate action. Treating people like this is completely abominable."
Onuoha, 24, has made 72 league starts for City and spent last season on loan at Sunderland. He signed a new five-year contract at Eastlands in 2009.