Ronaldinho could miss Brazil's friendly international against Argentina in London after injuring his back in training, coach Dunga said on Saturday.
A sellout crowd is expected at Arsenal's Emirates Stadium for Sunday's match with many of the 60,000 spectators expecting to catch a glimpse of the Barcelona maestro.
But Dunga revealed that, although the 26-year-old was due to belatedly link up with his squad on Sunday, he is unlikely to feature in the South American derby.
"When he was playing with Barcelona he had a problem with his thigh and managed to sort that problem out," he told a news conference at the match venue.
"But then in training he had a problem with his back and was having treatment from a physiotherapist to sort out the problem."
Dunga also said World Cup midfielder Kaka is not guaranteed a spot in his starting line-up during the new regime.
"He is not going to start just because he is a superstar. He will have to earn his place in the team."
Dunga, who captained his country to World Cup victory in the U.S. in 1994, said he understands the sheer magnitude of the task of coaching Brazil and the expectation levels that accompany the job.
'THE BEST'
"When you are asked to do this job, you do it with your heart. I know this is my calling.
"I had a great time in the Brazilian national team when I was a player and anyone who has been a player for Brazil realises that this is their calling.
"I know the expectations of being Brazil's coach, but in life you must have courage to do things and try things. As a player, I knew I wasn't the best, but I had to try things to become the best.
"As Brazil's coach, I have gathered a group of technical people to try and help me do my best. There is fear in life, in everything you do, but you just have to face it up front and have the courage to take on things."
Dunga is determined to beat Argentina in his second match in charge following a 1-1 draw with Norway in Oslo on Aug. 16.
He told Brazilian reporters in an informal chat on Friday that this was a good chance for Brazil's World Cup players to try to overcome the disappointment of underachievement in Germany where they went out in the quarter-finals.
"The important thing is to win. (Argentina coach Alfio) Basile has emphasised playing good football but everyone wants to win," Dunga said.
"What's in play (on Sunday) is supremacy in South American football. This match has awakened the same interest as a World Cup final."
Basile is taking charge of his first match as Argentina coach since ending his first tenure at the 1994 World Cup. he has replaced Jose Pekerman's side who lost on penalties to hosts Germany in the World Cup quarter-finals.