Portugal coach Fernando Santos says winger Ricardo Quaresma will be a game-time decision for Tuesday's Euro 2016 Group F opener against Iceland.
The Besiktas winger trained separately from the rest of the squad at the Stade Geoffrey Guichard on Monday.
Santos told a news conference: "There are still 24 hours to go and even 12 hours can make a difference. I will decide tomorrow whether he will play or not.... Right now I have no doubts he'll be among us.''
Quaresma, 32, scored twice and set up two more goals in the 7-0 demolition of Estonia last week, Portugal's final warm-up game.
Fenerbahce's Nani would replace Quaresma alongside Cristiano Ronaldo in attack.
Nani started just one of Portugal's three warm-up games, a 1-0 defeat by England on June 2, and was replaced by Quaresma after 61 minutes.
Ronaldo, who scored 51 goals in 48 games in all competitions for Real Madrid this term, was also bothered by muscular problems at the end of the season.
"He is very well. He is really motivated," Santos said of Ronaldo.
Portugal reached the semifinals four years ago before being eliminated by Spain on penalties.
After their opener, Portugal take on Austria on June 18 in Paris and Hungary four days later in Lyon.