The Real Madrid attacker has yet to fully recover from a thigh problem and tendonitis and is unlikely to be risked with the World Cup set to get under way next week
Portugal star Cristiano Ronaldo may be back in training, but his involvement against Mexico in Friday's friendly in the United States seems unlikely.
Portugal are sweating on the fitness of their star man ahead of the upcoming World Cup in Brazil as Ronaldo battles thigh and leg issues.
To say Portugal are heavily reliant on Ronaldo is an understatement and the absence of their captain at the showpiece would be catastrophic for Paulo Bento's side.
The 29-year-old Real Madrid talisman single-handedly carried Portugal through their World Cup play-off, scoring all four goals – including a stunning second-leg hat-trick – as they beat Sweden 4-2 on aggregate.
Such was the interest in Ronaldo's condition, the Portuguese Football Federation (FPF) moved to release a statement on Wednesday in an attempt to quell the growing doubts about his fitness.
The FPF said Ronaldo was battling a "muscle injury on the back of his left thigh as well as left-leg patellar tendonitis".
News of Ronaldo's thigh issue was common knowledge, but the revelation about his troublesome knee is sure to worry Portugal fans.
Ronaldo has trained in New York this week, but Bento is likely to err on the side of caution and leave him out against Mexico in Massachusetts, particularly with another friendly against the Republic of Ireland to come on Sunday.
Raul Meireles and Beto are battling thigh and leg issues respectively, while Ronaldo's Real Madrid team-mate Pepe is also struggling for full fitness.
Portugal have played just one pre-World Cup friendly so far, and missing Ronaldo, they were held to a goalless draw against Greece.
Bento's men open the World Cup with a tough clash against Germany on June 16.
Mexico are likely to play a full-strength side for this friendly, with coach Miguel Herrera previously stating that the team who started against Portugal would be the 11 he would depend on in their World Cup opener against Cameroon on June 13.
Herrera pulled no punches in describing Bosnia-Herzegovina as a "dirty" team following their 1-0 defeat in front of more than 60,000 fans in Chicago on Tuesday.
It followed 3-0 and 3-1 friendly triumphs against Israel and Ecuador respectively, as Herrera gave the likes of Manchester United striker Javier Hernandez and goalkeeper Alfredo Talavera the chance to impress.
Hernandez had several chances, but failed to score and Herrera is likely to revert back to a forward pairing that would include two of Giovani dos Santos, Oribe Peralta and Isaac Brizuela.
Luis Montes broke his leg against Ecuador and Mexico will be out to avoid further friendly casualties in their final pre-World Cup friendly.