Brazil president urges injured Ronaldo not to give up

Brazil's president Luiz Inacio Lula da Silva has urged international striker Ronaldo to keep his head up and work hard to overcome his latest career-threatening knee injury.

The 31-year-old Milan player underwent surgery on his left knee in Paris on Thursday after collapsing in pain during a game against Livorno in Italy, fuelling speculation the Brazilian's storied career may be over.

Lula, a self-described sports fanatic who peppers his speeches with soccer metaphors, said he and "millions of Brazilians" were saddened by Ronaldo's latest injury but also confident the three-times World Player of the Year would make another triumphant comeback.

"Young man, keep moving forward, be strong, don't give up," Lula said in an open letter to Ronaldo.

"I have faith, just as the Brazilian people do, that you will return to the playing field and once again you'll be an example of perseverance and courage."

Ronaldo, suffered a similar injury on his right knee while playing for Inter in 2000 but recovered to help Brazil to win a fifth World Cup in 2002.

In 2006, Ronaldo became the all-time leading scorer in World Cups with 15 goals in three tournaments. Since then, he has been plagued by injuries and has played sparingly.