The balky knee that limited Portugal star Cristiano Ronaldo during his pre-World Cup training may soon force him out of the tournament altogether.

Ronaldo, who experienced difficulties at practices in the days leading up to the 2014 World Cup, played the entirety of Portugal’s tournament opener against Germany on Monday. While the 29-year-old didn’t appear to experience much discomfort during the match, various reports claimed this week that he had been able to complete team practices ahead of Sunday’s game against the United States.

El Confidencial, a digital publication in Spain, claimed that Dr. Jose Carlos Noronha, a renowned Portuguese surgeon who specializes in knee injuries, told Ronaldo that he could face permanent injury if he attempted to play through the ailment.  “Let your knee rest, or your future is in danger,” Noronha told Ronaldo, according to El Confidencial, via NBC Sports.

But Noronha has denied El Confidencial's report. The surgeon told The Record, a Portuguese sports newspaper, that he never gave Ronaldo any such warning. Various media outlets, however, noted that Ronaldo limped off a practice field on Wednesday with a heavy bag of ice strapped to his knee before the scheduled conclusion of that day’s training.

 Neil Barker, a reporter for Omnisport News, claimed that Ronaldo participated in "90 percent" of Wednesday's practice and only applied the bag of ice near the end.

About a week before the start of the World Cup, the Portuguese Football Federation confirmed on its official website that Ronaldo had a “muscle injury on the back of his left thigh as well as left-leg patellar tendinitis,” also known as “jumper’s knee.”

It remains unclear if Ronaldo will attempt to play against the U.S. His absence would represent a sore blow to a Portuguese team that will already have to replace Pepe, a defender who received a red card (and subsequent one-game suspension) for delivering a headbutt to Germany’s Thomas Müller.

Portugal will face the U.S. in Group G action on Sunday, June 22 at 6 p.m. ET. The match can be viewed on ESPN.