Manchester City defender Dias, 27, had been out injured with a muscle strain suffered in the Premier League.
Sporting Lisbon's 17-year-old striker Geovany Quenda received his first call-up.
"At 17, being in the national team shows his potential," said coach Roberto Martinez, emphasising that the youngster's age "is not an impediment".
"What matters is quality, commitment and hard work," the Spaniard added in a press conference.
According to Martinez, the choice of those selected was "meticulous and professional".
"If I could call them all, I would do it because they deserve it, but it's not possible," he said, noting that defender Joao Cancelo of Al-Hilal and midfielder Otavio of Al-Nassr are injured.
Portugal will play Denmark on 20 March in Copenhagen and next Sunday in Lisbon.
Portugal's 26-man squad:
Goalkeepers: Diogo Costa (FC Porto), Rui Silva (Sporting Lisbon), Jose Sa (Wolverhampton/ENG)
Full-backs: Diogo Dalot (Manchester United/ENG), Nelson Semedo (Wolverhampton/ENG), Nuno Mendes (PSG/FRA), Nuno Tavares (Lazio/ITA), Gonçalo Inacio (Sporting Lisbon), Ruben Dias (Manchester City/ENG), Antonio Silva (Benfica), Renato Veiga (Juventus/ITA)
Midfielders: Joao Palhinha (Bayern/GER), Ruben Neves (Al-Hilal/KSA), Joao Neves (PSG/FRA), Vitinha (PSG/FRA), Bruno Fernandes (Manchester United/ENG), Bernardo Silva (Manchester City/ENG), Joao Felix (AC Milan/ITA)
Strikers: Francisco Trincao (Sporting), Francisco Conceicao (Juventus/ITA), Pedro Neto (Chelsea/ENG), Geovany Quenda (Sporting), Rafael Leao (AC Milan/ITA), Diogo Jota (Liverpool/ENG), Goncalo Ramos (PSG/FRA), Cristiano Ronaldo (Al Nassr/KSA)