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The Real Madrid star left the pitch with a thigh problem following a clash with goalkeeper Kiko Casilla.
"It was a minor scare, a knock, but in a few days I will be well," said Ronaldo, who has 51 goals this season.
Real Madrid face Atletico Madrid in Milan this weekend in a repeat of the 2014 final, which Real won 4-1.
Portugal forward Ronaldo, 31, has been plagued by a thigh injury that forced him to miss three games in April.
He came off at half-time during Real's final La Liga game of the season.
Cristiano Ronaldo says he will be fit to play in Saturday's Champions League final against Atletico Madrid after limping out of training on Tuesday.