Arsenal have put a timescale of at least six months on Walcott's recovery from a ruptured cruciate ligament suffered against Tottenham in the FA Cup.
That prognosis rules him out of Arsenal's title pursuit and England's finals campaign in the summer, four years after he was surprisingly omitted from Fabio Capello's World Cup squad for South Africa.
Walcott has had offers from surgeons who claim he could be back in time for Brazil, including one Scottish specialist with extensive experience of working in sport, but Wenger is sceptical.
Robert Pires, Abou Diaby and Emmanuel Frimpong have all suffered similar injuries to Walcott during Wenger's time at Arsenal, and he said: "We have enough experience on cruciates to know that unfortunately the minimum time to come back is six months."
Asked whether Walcott, 24, would be the same player on his return, Wenger said: "Yes. I'm convinced.
"Deep studies show that players around 25 with that kind of injury come back as normal. When you are over 29, 30 you do not ever come back exactly the same, but between 25 and 28 you come back to the level you had before.
"Theo is very strong mentally, and he deals with it as well as you can when you are confronted with this kind of situation."
The emergence of Serge Gnabry and Alex Oxlade-Chamberlain's return from injury means Wenger is well-stocked for wide players.
But Walcott was used as a central striker against Spurs and, with Nicklas Bendtner out until the end of the month, Arsenal are short of back-up for Olivier Giroud.
Wenger has been linked with Fulham's Dimitar Berbatov and Real Madrid's Alvaro Morata, and he said: "If something interesting turns up we will do it. It could be a loan. I do not want to go into specific names - it's always sensitive.
"At the moment I believe we have no shortage unless we have some other big injuries."
Arsenal's game at Aston Villa is live on Monday Night Football. Coverage begins at 7pm on Sky Sports 1