Portugal captain Cristiano Ronaldo wore a brace on his left knee and defender Bruno Alves missed training on Friday as coach Paulo Bento prepared his injury-hit squad for their crucial World Cup clash against the U.S.

Ronaldo had been a doubt to face Germany in their opening Group G game, but declared himself fit to play before failing to make an impact as the Portuguese suffered a 4-0 thrashing.

Reports said he appeared in good spirits at the training session, but Portugal's concerns are growing ahead of the crucial game in Manaus on Sunday.

Earlier in the week, goalkeeper Beto said he believed Ronaldo would be "100 percent fit" to face the U.S.

The Real Madrid star has reportedly been suffering from tendinosis in the knee in recent months, missing numerous La Liga games because of the knee issue and a related thigh muscle problem.