The 26-year-old, who saw a specialist in Spain on Sunday, has been troubled by the problem for a number of weeks.
A Liverpool spokesman said: "It was decided that he would need surgery on a torn cartilage in his right knee.
"This will be carried out later on Sunday and, as a guide, the usual rehabilitation period for this type of procedure is around six weeks."
His fitness will be closely monitored by Spain manager Vicente del Bosque, whose side's opening World
Cup game in South Africa is against Switzerland on 16 June.
Del Bosque must submit his final 23-man squad to Fifa by 1 June.
Torres, who joined Liverpool from Atletico Madrid in 2007, will also miss out on meeting his former club in the Europa League semi-finals.
The Spaniard has scored 22 goals in all competitions this season, despite being beset by various injuries.
He was sidelined for a month after a knee operation in January and before Christmas struggled with a groin injury.
Torres's absence for the closing stages of the season is the latest blow for Liverpool.
The debt-ridden club is up for sale and all but out of the running for one of the valuable Champions League places, with the Europa League their only chance of silverware.
It also gives Liverpool manager Rafael Benitez a major headache in attack, with potentially another seven games left to play in a season where goals have been hard to come by when Torres has not played.
Dirk Kuyt, who normally plays on the right of midfield, can play as a forward and has scored nine league goals this season.
Young French striker David Ngog has scored just four times in the Premier League during the current campaign, with his last league goal coming on 16 December in the 2-1 home win over Wigan.
Benitez also has 19-year-old Spanish striker Daniel Pacheco, who has made the occasional substitute appearance this season.
Story from BBC SPORT:
http://news.bbc.co.uk/go/pr/fr/-/sport1/hi/football/teams/l/liverpool/8628770.stm
