"I feel fine, there have been no complications, nothing that has restricted me from any training activities or game activities to present so I feel good," Onyewu told reporters at the team's countryside base near Pretoria on Tuesday.
"I am physically fit, I have had to do all the physical work with the team and even before that I had to do a fitness test in Milan in order to be considered for match fitness - there are no issues in regard to me being able to play a full ninety," he added.
The centre-half made his return to action in last month's friendly against the Czech Republic and also featured during the build-up games against Turkey and Australia but has not played a full game as coach Bob Bradley rotated his back-line.
"Obviously I would have loved to have been able to see if I could play a full ninety but as it is, a lot of the defenders didn't play a full ninety," he said.
"I think Bob has been trying to disperse the time as evenly as possible amongst the players and I don't have an issue with that," he said.
"It was a progression, the Czech game was my first game back after seven months and I could have anticipated that not being the greatest outing but you get better as you go and right now I feel fine and ready for this tournament," he said.
