Portugal were gearing up for the 2014 FIFA World Cup™ on Tuesday in New Jersey, fretting over the fitness of superstar Cristiano Ronaldo.

With the World Cup looming, the FIFA Ballon d'Or winner as best footballer of last year, had some bad news about his recent aches and pains. Ronaldo has a "muscle injury on the back of his left thigh as well as left-leg patellar tendinitis," the Portuguese Football Association said in a report on his medical issues and those of stars Raul Meireles, Pepe and Beto.

Amid some heavy downpours, the four spent their time at the New York Jets' training center grinding it out on different exercises meant to get them in the best possible shape in the final sprint before the World Cup starts 12 June.

While Portugal have previously discussed superstar Ronaldo's thigh injury -sustained late in the season - it was the first time they reported patellar tendinitis.

The Portuguese have been drawn in Group G at the World Cup and will face Germany on 16 June in Salvador, USA a week later in Manaus and then Ghana on 26 June in Brasilia.

"We hope that Cristiano is in good enough shape to play - and to help the team," team-mate Nani, who plays for Manchester United, told reporters.

Ronaldo "is going well, and he is relaxed about it ... Things are going the right way," he added, after hundreds of fans welcomed the team at the Newark airport in New Jersey, just outside New York City.

Portugal will play two friendlies while in the United States. They take on Mexico in Foxboro near Boston on Friday - at the home of the NFL's New England Patriots. Next Tuesday they face Ireland at the Jets' MetLife Stadium - which hosted the Super Bowl in February.

Nani, 27, who missed out on the last World Cup in South Africa due to a shoulder injury, said fitness woes can make a player "distracted and less sure of himself."

"If for some reason (Ronaldo) is not there, whoever is there playing has to be confident in their ability to get the job done," he said. "The World Cup is a one-of-a-kind challenge. I want to be fully fit, and in top form alongside my team-mates. I could not be there last time, but happily, I am here now," said Nani, who has played 73 games and scored 14 goals with Portugal's national side.

He said the first clash with Germany will be key to setting the tone for the rest of the tournament, preferably a winning one.