* Suarez had left knee cartilage damage
* Not ruled out of Brazil tournament
* Vows to regain fitness in time for Brazil (Adds Suarez quote, detail)
MONTEVIDEO, May 22 (Reuters) - Striker Luis Suarez promised Uruguay fans he would be at the World Cup finals after successful keyhole surgery on a knee injury on Thursday.
Suarez, who helped Uruguay to fourth place at the last World Cup in South Africa four years ago, will need 15 to 20 days to recover but Uruguay team doctors are not ruling him out of the tournament in Brazil, which runs from June 12 to July 13.
"Many thanks to all of you for your support. Relax, because I'll get there and work hard these days to be 100 percent to help my team mates," Suarez said on the local sports website ovaciondigital.com.uy.
"Yesterday... Luis Suarez, after the normal warm-up (for practice) felt an intense pain in his left knee... An MRI scan confirmed partial lesion of the external meniscus," a Uruguayan Football Association (AUF) statement said.
"This morning he had an arthroscopy with a partial resection of the meniscus, there was no evidence of other lesions in his knee... His participation in the World Cup in Brazil is not ruled out."
The statement said Suarez, top scorer in the English Premier League last season with 31 goals for Liverpool, sustained a knock in the club's final match of the season.
AUF board member Alejandro Balbi, who visited Suarez at his bedside, told Reuters: "He is fine, feeling strong and very hopeful of coming back the earliest possible."
The 27-year-old Suarez has little room for manoeuvre before Uruguay play their first match in Group D, against Costa Rica in Fortaleza on June 14. Uruguay also face England and Italy in the first round.
Suarez is expected to miss Uruguay's warm-up matches in Montevideo against Northern Ireland on May 30 and Slovenia on June 4.
"Be strong!! Get well soon @luis16suarez We're waiting for you!!" said fellow striker Edinson Cavani in a message on his Twitter account.
(Reporting by Nick Mulvenney in Sydney and Malena Castaldi in Montevideo; Writing by Rex Gowar in Buenos Aires Editing by Ed Osmond)