The 24-year-old has suffered an abdominal injury and will miss the Three Lions' vital upcoming double-header in October, as well as four matches for Arsenal
Arsene Wenger has confirmed the Arsenal forward will undergo a minor procedure on Wednesday and will be unavailable for "a few weeks".
Walcott missed the Gunners' 3-1 win over Stoke City, and will now sit out a crucial Champions League clash with Napoli as well as domestic encounters with West Brom and Swansea City.
"Theo will be out for a few weeks," Wenger told the club's official website. "He has developed some damage to his posterior abdominal wall. It's not a hernia, but it's a little structural problem in his abdomen.
"He will have the procedure in Germany on Wednesday and, because it’s so minor, we can begin his rehab immediately.
"We are pleased it’s being dealt with quickly and he shouldn’t miss too many Arsenal matches. But he will miss the forthcoming international matches with England."
The 24-year-old has started the season in impressive fashion and netted his first goal of the campaign in Arsenal’s recent 2-1 Champions League victory over Marseille.