Ronaldo suffered the injury following a crunching tackle from Dimitri Payet, with reports claiming the 31-year-old could miss Madrid's start to the LaLiga season.
But Madrid's all-time leading goalscorer took to Instagram to insist he is on the comeback trail.
"Hi everyone! I just wanted to thank all my fans," Ronaldo said in the video, having been seen on holiday with his left knee in a brace.
"I wanted to tell them that all is well and that I will come back much stronger.
"Thank you, long live Portugal!"
Ronaldo and a robust Payet collided early at the Stade de France, with the former's knee bearing the brunt of the force.
After limping off the field, the three-time Ballon d'Or winner tried to continue playing but he was unsuccessful, though Portugal still managed to go on and win thanks to substitute Eder's 109th-minute strike.
