The Sun reported that Walker and a friend hosted a party with some sex workers last Tuesday, and City released a statement condemning Walker’s breach of lockdown and social distancing rules.
"Manchester City FC are aware of a story in a tabloid newspaper regarding the private life of Kyle Walker in relation to a breach of the UK lockdown and social distancing rules," began the statement.
"Footballers are global role models, and our staff and players have been working to support the incredible efforts of the NHS and other key workers in fighting the effects of the Covid-19 coronavirus in any way we can.
"Kyle's actions in this matter have directly contravened these efforts.
"We are disappointed to hear the allegations, note Kyle's swift statement and apology, and will be conducting an internal disciplinary procedure in the coming days."
On Wednesday last week, Walker had posted an appeal on social media to the public urging them to follow government advice.
Walker said today in his own statement: "I want to take this opportunity to issue a public apology for the choices I made last week which have resulted in a story today about my private life in a tabloid newspaper.
"I understand that my position as a professional footballer brings the responsibility of being a role model. As such, I want to apologise to my family, friends, football club, supporters and the public for letting them down.
"There are heroes out there making a vital difference to society at the moment, and I have been keen to help support and highlight their amazing sacrifices and life-saving work over the past week.
"My actions in this matter are in direct contrast to what I should have been doing regarding the lockdown. And I want to re-iterate the message: stay home, stay safe."