Ancelotti spoke about the Frenchman in the press conference after Atletico Madrid.
Kylian Mbappe has generally had an extraordinarily good start to 2025 for Real Madrid, scoring goals for fun and making sure his team wins when it matters most.
It was the polar opposite of the figure Real Madrid fans were seeing in the first few months of the Frenchman's time at the club, where he was subject to ridicule because of offsides and lack of confidence on the pitch.
Mbappe did not have the best of games against Atletico Madrid in the Champions League, though, as he looked to be an isolated figure for most of the game, and often looked a bit tired physically.
Ancelotti had a couple of reasons for why Mbappe was not at his best, one of which was a health problem, while the other was a tactical issue.
Not training for three days cannot be an excuse for a player like Mbappe to miss a simple pass that could have doubled Real Madrid's lead, but Ancelotti did say after the game that was why he may have looked out of it. The tooth extraction bothered him enough to miss training, and it is taking a little bit of time for him to come back to the swing of things.
He said: "It's just the tooth extraction. He hasn't been able to work much, because the toothache hasn't allowed him to work for three days. He didn't arrive at the game against Betis in his best condition and these minutes have been good for him to be in optimal condition for the next games."
When asked further about whether there were any other problems that he faced during the game, Ancelotti mentioned the tactical side of things, and how Atletico made it difficult for the Frenchman to get into the game.
He said: "No, he was fine. He didn't have any problems. They did a good job defensively because they tried to be compact with the team. When they get into a good position, it allows the two midfielders to be closer to the defence and help more in defence."
This was an opportunity for Mbappe to see what is working and what isn't, and one would assume that he would be much, much better than this when Real Madrid travel to the Wanda Metropolitano to face their city rivals in the return leg.