Man City defender Stones out for a month
City's defensive options had already been hit by Aymeric Laporte being ruled out for six months by a knee injury, while no replacement was signed for departed club captain Vincent Kompany.
That left Stones and Nicolas Otamendi as City's only senior centre-backs and the pair looked shaky last time out as City went down to their first Premier League defeat since January, losing 3-2 away to promoted Norwich City.
City will be further stretched for the upcoming period after Guardiola told reporters ahead of a Champions League trip to Shakhtar Donetsk that Stones was injured in training on Tuesday.
"A month, four or five weeks," Guardiola said when asked how long Stones would be out.