Cristiano Ronaldo will make his bow at Euro 2016 and begin what could be his last realistic opportunity to add a major international trophy to his collection of both club and individual honors. It's barely over two weeks since the three-time Ballon d’Or winner scored the winning penalty for Real Madrid to secure a third Champions League winners’ medal. But with Portugal the closest he has come was a heartbreaking loss in the final of his first international tournament, 12 years ago.

Now, at the age of 31 and with signs that his pure physical peak has already moved slightly behind him, the world’s most famous athlete will attempt to leave an indelible mark on a major international competition. To do so, he will have to overcome doubts over his fitness. Despite producing the winning moment, Ronaldo was clearly not at his physical best in the Champions League final, having suffered a left-thigh injury in the days leading up to the game. It was a similar scenario heading into the 2014 World Cup, when Ronaldo started all three games despite not being close to full fitness, and Portugal crashed out at the group stage.

Portugal coach Fernando Santos has played down any injury fears but admitted that Ronaldo, who endured a long season with Real Madrid in both La Liga and the Champions League, may not be competing at his best. 

"Look, there is always talk about all the players having to arrive at 100 percent, but that is never the reality," Santos told Marca. "In football, that is not what happens. There are always exceptions. Obviously, the ideal thing would be for him to be at his best, but I would never leave out a Cristiano at 80 percent. We have looked closely at the preparation so that he does not get more tired. It would be different if he had an injury.

"If we were not sure he would be able to last a game, we would not call him up. I know how he arrived after the Lisbon final [2014] and his problems."

On Tuesday, the superstar will go up against the Cinderella story of the tournament, Iceland, in Saint-Etienne. In Portugal's first group match, the pressure may be on Ronaldo to help his country gain momentum in one of the weaker groups of the tournament.

Ronaldo has come a long way since gracing his first European Championship. At Euro 2004, held in his home country, he was still a raw teenager, fresh from his first season at Manchester United. With Portugal he still had more-established stars around him, notably Luis Figo, Deco and Rui Costa. Still, with two goals, Ronaldo offered plenty to suggest he would soon be the main man, despite his side being upset by Greece in the final.

Ever since then, the Portugal team has increasingly revolved around the man who has marked himself down as one of the all-time greats. The question for every Portugal coach has been how to get the best out of Ronaldo, particularly in a team where the lack of a top-class center-forward has caused a constant headache.

For a long time, Ronaldo did not want to play through the middle, preferring to stick to the position he has long occupied on the wing with his clubs. But now, as his changing physical condition has led him to become less of a winger and more of a penalty-box striker, he is ready to fill the void for his country.

His current coach has had a big impact in his short time in charge. The former Greece coach, brought in after a 1-0 loss to Albania in September 2014, won all seven of his qualifiers at the helm to guide Portugal to France. And for Euro 2016 he is set to unveil his tactical attempt to get the most from Ronaldo and his team. Rather than the 4-3-3 that Portugal coaches have so often gone with, aiming to make the most of the country’s habitual ability to produce tricky wingers, Santos looks likely to opt for a 4-4-2 and two wingers up front.

For the opener, Ronaldo is expected to line up alongside Ricardo Quaresma, pairing together two players who burst through the youth ranks at Sporting Lisbon together. Many believed that Quaresma was the more talented, but, helped by his supreme dedication, it is Ronaldo who has gone on to enjoy the far greater career.

For both men, though, Euro 2016 is now a chance to make a lasting mark on a major tournament. They certainly showed what they are capable of when scoring two goals apiece in Portugal’s final warmup game against Estonia last week. Like Ronaldo, though, Quaresma has questions hanging over his fitness, and faces a race to recover from a thigh injury for the opening game. 

Iceland will be the underdog aiming to exploit any vulnerabilities. The country of a little more than 320,000 people became the smallest ever to make it to a major international tournament, finishing ahead of both the Netherlands and Turkey in qualifying. But Iceland is not just along for the ride, and has already taken a shot at Portugal and its star man in the buildup to its debut on the big stage.

“We’ve seen some Portuguese players diving,” coach Lars Lagerback, formerly coach of Sweden, said. “Portugal has one of the best players in the world in Ronaldo, but he’s also an excellent actor.”

Prediction: Portugal has been far more tactically sound under Santos, all starting with a solid backline. In his seven qualifiers in charge, Portugal conceded just four goals. From there the plan is simply to get the ball to Ronaldo, and to a lesser extent Quaresma, or, if he doesn’t win his fitness battle, Nani. The positive of Ronaldo being up front rather than on the wing is that his lack of work rate off the ball should compromise his team far less. Expect Iceland, in a 4-4-2, to be rigid and attempt to frustrate Portugal and hope for some creative inspiration, either from open play or set-pieces, from Swansea City’s Gylfi Sigurdsson. It could well be a tight affair, with Portugal just sneaking a win.

Predicted Score: Portugal 1-0 Iceland

Kickoff Time: 3 p.m. EDT

TV Channel: ESPN

Live Stream: Watch ESPN