Ronaldo was provisionally suspended by the Portuguese Football Federation after walking out of the national team camp following a bitter dispute with head coach Jorge Jesus.
The former Manchester United and Real Madrid star apologised for his actions but insists the manager broke his word to him over his playing time against Norway in the Nations League.
Questions were raised over whether Ronaldo would play for Portugal again as he awaits his punishment, which reports suggest could be a suspension of a few months and a small fine.
As Ronaldo waits to hear the verdict, Proenca has spoke on the legendary forward, who he says is still crucial to the nation's success.
"We are in the home of the greatest asset Portuguese football has ever produced: Cristiano Ronaldo, our captain," Proenca said, as quoted by ESPN.
"Our captain, Cristiano Ronaldo, is one of our key pieces."
Portugal will next face Denmark and Wales in the Nations League and depending on his punishment, Ronaldo could be suspended for both games, despite Proenca's statement this week.