By Julien Pretot
PARIS, Jan 23 (Reuters) - Colombia striker Radamel Falcao's hopes of participating in the World Cup finals hung in the balance on Thursday when his Ligue 1 club Monaco announced he would undergo surgery on a left knee injury.
Monaco did not elaborate on the length of Falcao's absence, but the Spanish news agency EFE reported that the 27-year-old forward could be out for six months.
"Radamel Falcao suffered a lesion on his left knee's cruciate ligament. Surgery is necessary... the doctors will do everything they can to help Radamel Falcao recover as quickly as possible," Monaco said in a brief statement.
A spokesman told Reuters by telephone that the club could not say anything more for the moment.
Falcao picked up the injury after scoring his team's first goal in a 3-0 win at amateurs Chasselay Monts d'Or Azergues in a last-32 French Cup game on Wednesday.
Falcao was a key member of the Colombia side that coach Jose Pekerman steered to second place in the South American qualifying group and a direct place as one of the seeded nations for the finals, which start on June 12.
He top-scored for Colombia with nine goals and forged a good partnership up front with Teofilo Gutierrez which yielded a tally of 15.
Colombia, looking to reach the finals for the first time since 1998 in France, did not, however, make a good start to the qualifiers.
After a 2-1 home defeat by Argentina in Barranquilla in November 2011 had left them with four points from their opening three matches, coach Leonel Alvarez was sacked.
Argentine Pekerman, who had steered his country to the 2006 quarter-finals in Germany and was well known in Colombia after spending three years of his playing career there with Independiente Medellin, took the reins in 2012.
After a 1-0 win away to Peru and a 1-0 defeat in Ecuador in June 2012, Pekerman's side took off with a 4-0 home rout of Uruguay in which Falcao gave them the lead after two minutes.
Colombia won six and drew two of their remaining 10 qualifiers to finish two points behind favourites Argentina.
A key element in Colombia's success was Pekerman's faith in James Rodriguez as the most advanced midfielder, feeding the strikers or running into space to score three himself.
The combination of Falcao and Rodriguez for Colombia was not lost on Monaco who swooped for both from Atletico Madrid and Porto respectively when they were promoted and rebuilt for an assault on Ligue 1 this season.
Falcao's possibly long absence is also likely to seriously dent Monaco's Ligue 1 title bid.
The Colombian, who joined from Atletico Madrid during the close season for a fee exceeding 50 million euros, has scored nine goals from 17 league appearances.
Monaco are second in Ligue 1 with 45 points from 21 games, five adrift of French champions Paris St Germain. (Additional reporting by Etienne Ballerini and Rex Gowar; Editing by Justin Palmer and Pritha Sarkar)