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Although his knee had been bandaged in previous practice sessions, Ronaldo started without one on Wednesday. After some light work with the rest of the first team followed by some stretching, the world player of the year had the knee ice-packed.
He then waved and distributed some T-shirts to a crowd of some 3,000 fans before leaving with the rest of the squad.
Ronaldo was doubtful to play before Portugal's opening 4-0 defeat to Germany but said before the Group G opener that he was fully fit. Portugal will face the U.S. on Sunday in Manaus, Brazil, at 6 p.m. ET.
Trainers applied ice to Ronaldo's knee, and he watched the final portion of practice from the bench, according to Portuguese sports daily Record.
"Cristiano is 100 percent fit to play. Every match, if he starts to play, it is because he is fit to play, he's ready to play,'' Beto said. ''He loves football, but his body is the most important thing for him ... so if he starts a match he is ready, he is fit, so I don't think that is a problem.''
Ronaldo has been bothered by several leg complaints throughout his latest club season, in which he led Real Madrid to their record 10th UEFA Champions League title.
He played in the final against crosstown rivals Atletico Madrid -- scoring a penalty late into extra time -- then rested in a bid to be ready for the World Cup.
Ronaldo made his return to the field just under two weeks ago in a friendly win over Republic of Ireland, then played the full 90 minutes against Germany in the Group G opener.
Ronaldo has frequently left training early to ice his knee over the past several weeks. The Portuguese federation has not commented.
Information from The Associated Press was used in this report.
Ronaldo leaves practice early
Portuguese forward Cristiano Ronaldo was forced to leave practice early due to his troublesome knee issue.
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