Saitama, Japan:A left thigh injury could force Ronaldo to miss Brazil's upcoming World Cup semifinal match, team doctor Jose Luis Runco said Saturday. Runco said an ultrasound showed Ronaldo had a stress injury on his left thigh but that there was no muscle tear. "There was no rupture of muscle fiber," he said. "Nothing is certain. If it doesn't improve with treatment then he won't be released for Wednesday's match. Sometimes muscle injuries take longer than we expect. Only time will tell, but it's not a serious injury." Brazil will face the winner of the Senegal-Turkey match in Wednesday's semifinal. Runco said Ronaldo wouldn't practice Sunday, but could rejoin the team on Monday, depending on the pace of his recovery. The 25-year-old Internazionale star played down the problem. "It's nothing to worry about," said Ronaldo, who was substituted in the second half of Brazil's 2-1 quarterfinal win over England because of his sore leg. "Now we have time to recover." Runco said the injury was unrelated to any of Ronaldo's knee problems that had disrupted the star's career for the past two years. "Since March, Ronaldo has been in the same condition as any other athlete," Runco said. "This is a common problem which could affect any footballer." Ronaldo has scored five goals at the 2002 World Cup and is tied with teammate Rivaldo and Germany's Miroslav Klose in the race for the Golden Boot. Ronaldo's injury is a serious worry for the squad, who will be without another of its stars, Ronaldinho, sent off during the team's quarterfinal match against England, after coming in studs up on a ball and hitting defender Danny Mills instead.