However, after a return to the Arsenal team, Walcott was called up to the England squad for the friendly against Egypt, and started at Wembley on Wednesday night before being replaced by Shaun Wright-Phillips after an ineffectual display.
Walcott - who smashed a famous hat-trick in the qualifier against Croatia at the start of last season - admits he cannot rely on past glories to make sure of his place in Fabio Capello's final 23-man party for South Africa.
Wenger, though, feels the former Southampton man - a shock inclusion in the last World Cup squad four years ago - is on the right track, despite being an easy target for critics.
"I believe for a while maybe people expected too much of Theo and now they are too hard with him," said the Arsenal manager.
"I believe Theo will be a great football player, he is very young, he will be 21 this year, he will have a great future.
"I believe in him because he has a fantastic attitude, he's an intelligent boy and he is highly motivated. These players always improve."
Former England winger Chris Waddle questioned Walcott's England credentials, claiming the youngster "doesn't understand the game".
Wenger, however, defender his player.
"Don't worry for him," the Arsenal boss said.
"I believe Theo has not only a football brain, but he has a brain - that means he will continue to develop at a very quick pace."