Real Madrid have been struggling with injuries and form all season, and there have been points where those two have coincided. They just have not been the team they so obviously can be, but are still not ruled out of any competition, which is a testament to them in a way.
However, Real Madrid, even in form, have had a lot to deal with in terms of fitness. Jude Bellingham, Vinicius Jr and Rodrygo were all carrying knocks after the Rayo Vallecano game, and now, according to reports in Spain, Mbappe is also carrying one.
Kylian Mbappe is dealing with a muscle overload, he may start against Atletico but it is not guaranteed
According to COPE, Real Madrid's number nine suffered a blow against Rayo, and although he is not completely ruled out of the match against Atletico Madrid, his place in the starting XI is not guaranteed.
According to Miguel Angel Diaz, Mbappe will undergo tests tomorrow to determine whether he can start. The only reason Real Madrid have not announced the squad yet is because of this new knock that Mbappe has suffered, and it will be confirmed soon.
If the Frenchman misses the match, it will probably be Brahim Diaz who starts in his place. However, even he has been going through an illness in the last couple of days, and it was reported that his place in the squad is not guaranteed either.
Real Madrid have to get through this Atletico test and they will then have some breathing room, as there are no Champions League matches until the second and third week of April.
It remains to be seen whether Mbappe actually starts, because even though he has not been at his best in the last couple of games, his importance and quality cannot be questioned. On his day, he is the most dangerous player on the planet, and even though he was not good in the first leg, there is no reason for him to repeat that performance in the second.