Walcott suffered a ruptured anterior cruciate ligament of his left knee during Arsenal’s 2-0 FA Cup win at home to arch north London rivals Tottenham Hotspur on Saturday.
An Arsenal statement said Walcott is “expected to be out for at least six months, therefore missing the remainder of the (English) season and the World Cup in Brazil in the summer”.
The 24-year-old Walcott jarred his knee towards the end of the match making a tackle and was carried from the field.
Whilst on a stretcher, Walcott was pelted by coins and plastic bottles, among other objects, from the away end.
Earlier on Monday and before the extent of his injury was made public, the Football Association (FA), the English game’s governing body, said Walcott would not face disciplinary action for making a ‘2-0’ gesture from his stretcher that appeared to be aimed at Spurs fans.
“The FA has contacted both Arsenal and Tottenham Hotspur to seek their observations in relation to objects being thrown from both a home and away section of the crowd at different times during Saturday’s FA Cup third round tie.
“The FA condemns any such acts and will liaise with both clubs and the Metropolitan Police to identify those responsible and support the strongest sanctions available, including life bans.
“Meanwhile, in relation to the same fixture, The FA has contacted Arsenal’s Theo Walcott and reminded him of his responsibilities regarding a ‘score-line’ gesture he made in front of away supporters during the game. The FA will not be taking any further disciplinary action.”