Andre Santos will also miss the game with an abdominal strain, manager Arsene Wenger told reporters on Tuesday.
Left-back Kieran Gibbs and Ivory Coast forward Gervinho return from injury and are in the squad, who are buoyed by their 5-2 win over Spurs.
"He [Walcott] injured his shoulder in the game and we have to scan that and see if there is no damage. It should be short-term," Wenger said.
"We will miss Andre Santos as well as he has a muscle strain in his abdomen."
"To his defence I must say last year he arrived on August 31, and had no pre-season, had an ankle injury and had to adapt to a completely new world," the Frenchman told reporters.
"Centre-back is difficult for people who come from abroad, it was a bit of a shock for him, but this season he has come back very fit, well prepared, and of course knew what the expectations were for him and did extremely well.
"This season especially, as you [the media] have noticed, he has been outstanding. The criticism was always completely unjust. It was overboard, we always say you have to deal with that."
