Ronaldo’s name was notable for its absence when Portugal coach Fernando Santos announced the line-up last Friday.
Santos said the 31-year-old is still recovering from the knee injury he sustained during the first half of the Euro 2016 final against France.
The coach explained his choice was “to maintain the base of the final stages of the European championship, apart from the ones who are medically not in shape.
“The national team is never closed to any player”, he added, stressing: “There are other options who could be here but aren’t today.”
Portugal take on Switzerland in Basel next Tuesday, 6 September, in their opening game in Group B, five days after playing a friendly against Gibraltar in Porto on Thursday.
It will no doubt be of some consolation that ‘Madeira’s most famous son’ was awarded the UEFA Best Player in Europe award for a second consecutive time last week.
Ronaldo took the 2015/2016 title after winning the UEFA Champions League with Real Madrid and the EURO 2016 tournament with Portugal.
It is the second time the Real Madrid and Portugal forward lifted the UEFA Best Player in Europe Award after first lifting it in 2013/14.
He beat off competition from club-mate Gareth Bale and Atlético Madrid striker Antoine Griezmann.
Speaking to UEFA after the award, Ronaldo said: “It’s a great honour. My team-mates are the key – they are the key every year. I work hard myself but without their help this would not be possible. Thanks to my team-mates from Real Madrid and Portugal. [Winning the Euro] was different because I’ve won the Champions League three times now. To win something with Portugal was the highlight of my career.”
The recipient of the UEFA Best Player in Europe award is decided after journalists from each of UEFA’s 55 member associations vote on an initial list of their five best-ranked players.
The ten players with the most points advanced to a second round of voting, which determined Ronaldo, Bale and Griezmann as the final three.
In a live poll during the UEFA Champions League group stage draw, the same 55 journalists then selected their favourite from the three-man shortlist via an electronic system.