Walker came into the tournament as an injury doubt, despite having made a remarkable recovery from a groin injury suffered during the Manchester derby against Manchester United in October.
Walker had said in the past few days that he expected to miss the Iran game, but believed he would be ready to go after that.
Maddison limped off for Leicester City during the final match before the break for the World Cup, and has since missed three training sessions in a row - and will also miss the Iran match.