The northwest club said that the 24-year-old would be out for between six to eight weeks. He damaged his cartilage while changing direction in Saturday's match, which City won 1-0, and no other player was involved.
Richards has played four times this season and had only recently returned from a serious heel injury. City are already without defenders Maicon and Pablo Zabaleta, although the Argentinian could return for this weekend's match against West Ham.
Source: AFP
