Manuel Pellegrini expects to be without Joe Hart and Raheem Sterling for at least a month after both were injured in the Manchester derby.
Sterling damaged his groin during the first half of City's 1-0 defeat to United, while Hart was stretchered off after the break after injuring a calf muscle.
Both injuries will need further assessment, but in the aftermath of the game Manuel Pellegrini told Sky Sports: "Muscle injuries are never less than a month."
Asked in his press conference how long it would take the pair to recover, he said: "I don't think you can recover from a muscle injury in one week, normally it takes three or four weeks so I don't think they can play."
That timescale would rule both players out of England's upcoming games against Germany and the Netherlands and City's Champions League quarter-final against Paris Saint-Germain.
City also face Bournemouth, West Brom, Chelsea and Newcastle in the Premier League in the next month as they battle to hold on to a Champions League position.
United's victory at the Etihad took them to within one point of their rivals, while West Ham are also a point behind.