
Gray was carried off the pitch after he caught his left leg in the turf in Leicester’s League Cup victory over Wolverhampton Wanderers on Tuesday.
“He will be out of the squad for between three and six weeks, then we shall see if he can recover quick,” Puel told reporters on Thursday.
“It is a sprain, not a break… it isn’t serious, he needs rest and rehabilitation,” the Frenchman added.
Gray, 22, has played in all Leicester’s six league games this season and was called up to England’s squad for the friendly against Switzerland this month but did not make his debut.
Leicester are ninth in the league with nine points after six games, while Newcastle are 18th and still seeking their first win.