Ronaldo missed pre-season due to a knee injury picked up in the Euro 2016 final, but after just two games, he picked up the flu and missed Real Madrid's game against Espanyol on Sunday.
Meanwhile, Gareth Bale picked up a hip injury in Real Madrid's 2-1 victory in the Champions League against Sporting Lisbon, but has returned to training today.
They both could now face Villearreal on Wednesday at the Bernabeu.