After missing three games in a row with a groin problem, Grealish was deemed fit to start in the Citizens' 6-2 victory at Luton Town in the FA Cup fifth round on Tuesday.
However, the 28-year-old suffered a recurrence of his groin injury and was withdrawn in the 38th minute at Kenilworth Road where he was visibly upset and consoled by his teammates as he took his seat on the bench.
Grealish is now facing another spell in the treatment room after Guardiola revealed at a press conference on Friday that the attacker will not be involved in Sunday's Manchester derby.
«He will not be fit this weekend,» Guardiola told reporters. «When he comes back, I don't know. Setbacks are always there in life, he will overcome it.»
Asked if Grealish will be ready to return for England duty later this month, Guardiola added: «No. I need to speak with [England boss] Gareth [Southgate], I think he will not be fit.
»He has to recover well. He has had a setback, he has to recover well so we can use him as much as possible."
Southgate is soon expected to announce his latest squad ahead of international friendly fixtures against Brazil on March 23 and Belgium on March 26.
As well as the Manchester derby, Grealish is set to miss the second leg of Man City's Champions League last-16 tie with Copenhagen at the Etihad next Wednesday.
Grealish has also emerged as a major doubt for a Premier League trip to title rivals Liverpool on March 10 as well as an FA Cup quarter-final home clash with Newcastle United six days later – City's final match before the international break.
Meanwhile, it remains
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