The Arsenal forward suffered a cruciate ligament injury in the 2-0 FA Cup third-round victory over London rivals Tottenham earlier this month.
Arsenal released a statement two days after the match saying that they expected him to be sidelined for "at least six months", but could not confirm the duration of his absence.
Walcott went under the knife this week and although Wenger stated that the operation had gone "very well", he warned there is no chance of the England international returning ahead of schedule.
Wenger told Arsenal Player: "The damage was real in the knee so he will have to take the needed time, so let's not be hopeful that he will go to the World Cup - that is not possible, but overall his long-term future is very positive.
"It is about being fit for next season now."
Walcott's absence is a blow for both club and country, but manager Wenger is confident the London club have the strength in depth to cope without the former Southampton man.
He added: "In midfield we have plenty of quality players who you can rotate easily without really feeling, 'today we are weaker'.
"We have fantastic players in midfield and it always allows us to keep what we call the 'engine' of the team fresh.
"It is a real team effort. Maybe because every player in his position has a strong personality as well - you have that feeling.
"I would say purely on the football front it's true that we only have excellent players in every position and that allows you to have different types of teams that can really be efficient."
