Cristiano Ronaldo Injury: Knee Tendinitis Could Limit Portugal Star At 2014 FIFA World Cup [PHOTO]

A nagging knee injury could limit the effectiveness of one of soccer's most dominant offensive forces at the 2014 World Cup.

Cristiano Ronaldo, a striker for Portugal’s national team, has lingering issues with his left thigh and knee, the Portuguese Football Federation revealed on its official website on Tuesday, via ESPN. The organization characterized Ronaldo’s injury as a “muscle injury on the back of his left thigh as well as left-leg patellar tendinitis.”

The condition of Ronaldo’s thigh was already well publicized, but Tuesday’s announcement marks the first public acknowledgement of his bout with patellar tendinitis, or “jumper’s knee.” The knee injury casts doubts over the extent to which he’ll be able to contribute to Portugal’s quest for the World Cup, which begins with the nation’s Group G opener against Germany on June 16. However, his teammate, Portuguese winger Nani, remains optimistic.

“We hope that Cristiano is in good enough shape to play—and to help the team,” Nani told FIFA.com. “If for some reason he is not there, whoever is there playing has to be confident in their ability to get the job done. The World Cup is a one-of-a-kind challenge. I want to be fully fit, and in top form along with my teammates.”

Nani added that Ronaldo remains “relaxed” about his playing status.

The 29-year-old forward reportedly worked out at the New York Jets Training Center on Tuesday, ESPN reports. Mais Futebol noted that Ronaldo “appeared to be making progress.”