England scrumhalf Alex Mitchell has been ruled out of Saturday's Six Nations clash against Scotland due to a knee injury, with Harry Randall coming in as his replacement, the Rugby Football Union said on Sunday.While Mitchell's injury is a blow, England have received a boost with the return of centre Ollie Lawrence, who missed the first two games against Italy and Wales through injury.Marcus Smith will join up with the squad as the flyhalf continues his rehabilitation from injury.ENGLAND SQUADForwards: Ollie Chessum (Leicester Tigers), Dan Cole (Leicester Tigers), Alex Coles (Northampton Saints), Luke Cowan-Dickie (Sale Sharks), Chandler Cunningham-South (Harlequins), Ben Curry (Sale Sharks), Theo Dan (Saracens), Alex Dombrandt (Harlequins), Ben Earl (Saracens), Charlie Ewels (Bath Rugby), Ellis Genge (Bristol Bears), Jamie George (Saracens), Joe Heyes (Leicester Tigers), Maro Itoje (Saracens), Joe Marler (Harlequins), George Martin (Leicester Tigers), Beno Obano (Bath Rugby), Ethan Roots (Exeter Chiefs), Will Stuart (Bath Rugby), Sam Underhill (Bath Rugby)Backs: Danny Care (Harlequins), Elliot Daly (Saracens), Fraser Dingwall (Northampton Saints), Immanuel Feyi-Waboso (Exeter Chiefs), George Ford (Sale Sharks), Tommy Freeman (Northampton Saints), George Furbank (Northampton Saints), Ollie Lawrence (Bath Rugby), Max Ojomoh (Bath Rugby), Harry Randall (Bristol Bears), Tom Roebuck (Sale Sharks), Henry Slade (Exeter Chiefs), Fin Smith (Northampton Saints), Ben Spencer (Bath Rugby), Freddie Steward (Leicester Tigers), Manu Tuilagi (Sale Sharks)Rehabilitation:Marcus Smith (Harlequins)