Cristiano Ronaldo returned to training on Tuesday despite having to contend with patellar tendinosis as he seeks to return in time for Portugal's opening World Cup game against Germany.

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The Portuguese FA (FPF) announced on its official website that Ronaldo is suffering with a "muscle injury on the back of his left thigh as well as left-leg patellar tendinosis" as he works to be available for the Group G opener on June 16.

The Real Madrid star's thigh problem had already been made public but the news of the patellar tendinosis represents a new concern.

The FPF said he was working on building up his fitness out on the field at the New York Jets' training centre on Tuesday along with Raul Meireles and Beto, who are dealing with thigh and leg injuries respectively. Ronaldo was able to work with the ball and Mais Futebol reported that he "appeared to be making progress."

The 29-year-old's Madrid teammate Pepe, meanwhile, underwent treatment on his leg injury at the team hotel.

Portugal winger Nani was quoted on FIFA.com as saying Ronaldo was "going well" and is "relaxed" about his fitness troubles.

"We hope that Cristiano is in good enough shape to play -- and to help the team," Nani, who played alongside Ronaldo at Manchester United, said. "If for some reason he is not there, whoever is there playing has to be confident in their ability to get the job done."

Portugal also face the United States and Ghana in Group G.