Man City boss Mancini admits Richards out for month
Richards suffered the setback when on Olympic duty for Great Britain in the quarter-final clash with South Korea.
"He has a problem with his ankle, a big problem maybe, and it may be one month out."
Goalkeeper Joe Hart was also ruled out with a back problem which has also meant he is not available for England's friendly with Italy on Wednesday.
Mancini said: "Joe had a problem yesterday with his back but I don't think it is serious."