(Reuters) - Ronaldinho is in a race against time to be fit for the Club World Cup in December after suffering a serious groin injury, South American champions Atletico Mineiro said on Friday.

The Brazilian team's doctor Rodrigo Lasmar said the former Barcelona and AC Milan playmaker had felt pain in his left adductor muscle during training on Thursday.

"After clinical exams and a scan we confirmed he had totally ruptured the adductor muscle of his left thigh," Lamar told the club's official website (www.atletico.com.br).

He added that Ronaldinho was having intensive physiotherapy, with club president Alexandre Kalil quoted as saying Ronaldinho would have "wartime treatment", Globo reported on its website(www.globoesporte.globo.com).

Atletico reached the Club World Cup in Morocco, in which their first match is scheduled for December 18, by winning South America's Libertadores Cup for the first time in July.

They are favourites to meet Europe's Champions League winners Bayern Munich in the final.

"It's a grave injury," said Lasmar. "The recovery time is not short, it's around two and a half months, three months, three and a half months.

"The big question being asked is whether he'll be able to play the (Club) World Cup. I believe it's possible."

Ronaldinho looks set to miss the rest of the Brazilian championship which ends on December 8.

Atletico are eighth with 32 points from 23 matches, 18 adrift of leaders Cruzeiro, their arch-rivals in their home city of Belo Horizonte. They are at home to Santos on Sunday.

(Reporting by Rex Gowar in Buenos Aires; Editing by Ken Ferris)