Real Madrid forward is in a race against time to feature against Bayern in their crunch Champions League semi-final first-leg tie.
Despite training with his teammates today following a knee injury Ronaldo will have a test on the day of the game.
Ancelotti has at least Gareth Bale to potentially fill the void should 'CR7' miss out. The Welsh winger has impressed since arriving at Los Blancos last summer and his manager expects him to get even better next season.
He said. '[Bale] is going to improve next season. When he starts to train with us in the summer he will not have to play at the World Cup. I think next season he will be better. We can be really happy for next season.'
While Bale can have a big impact on the match with Bayern, Real will still have a greater chance of progressing to the final with Ronaldo back in the side.
Remember the former Manchester United player has much more big game experience and thrives under pressure, which there will be plenty of in this titanic match-up.
If Ronaldo features it means Pep Guardiola's players become more preoccupied with him which may leave more space for the likes of Bale to operate in, thus increasing Real's chances of scoring goals and building up enough of a lead to take into the second-leg over in Germany.
Whatever happens with Ronaldo however, this game is sure to have plenty of incidents and talking points.