The now unattached superstar had only been give a ‘50/50’ chance by head coach Fernando Santos of featuring in the final Group H tie at Education City Stadium in Al Rayyan due to an unspecified knock that has limited him in training this week.
Ronaldo is said to have been suffering from knee pain after the win over Uruguay and his status to face South Korea was very much up in the air.
With Portugal already through to the last-16 stage with a game to spare, Santos must feel confident starting his captain and talisman against Korea.
"I think it is 50-50 if he plays or not, we'll see," he said on Wednesday. "It will depend on if and how he practices today, if we see he is in good condition. There is a plan for if he is not available."
Rafael Leao does not start, but Diogo Dalot is handed a World Cup debut.
For Heung-min Son and company, it’s a fairly simple equation. While they are reliant on other results, anything less than a victory would end their World Cup campaign.
Such is the importance of the game, Paulo Bento does not make many changes, though will not be on the touchline himself after being sent off against Ghana.
Confirmed team news
South Korea: Kim Seung-gyu, Kim Moon-hwan, Kwon Kyung-won, Kim Young-gwon, Kim Jin-su, Lee Jae-sung, Lee Kang-in, Jeong Woo-yeong, Hwang In-beom, Son Heung-min, Cho Gue-sung.
Portugal: Diogo Costa, Diogo Dalot, Pepe, Antonio Silva, Joao Cancelo, Matheus Nunes, Ruben Neves, Vitinha, Joao Mario, Cristiano Ronaldo, Ricardo Horta.