Manchester City manager Pep Guardiola has revealed that John Stones will be sidelined for "a while" after being forced off in Tuesday's Champions League win over Young Boys.The European champions produced a dominant display to book their place in the knockout rounds with two games to spare.Erling Haaland, who was an injury doubt before the matche, opened the scoring from the penalty spot, before Phil Foden doubled the advantage in first-half stoppage time.