Mbappe has scored just one goal in his last seven Madrid games across all competitions and is also involved in a multi-million euro pay dispute with former club Paris Saint-Germain.
Ancelotti was asked at his weekly press conference if the striker was struggling with pressure.
"What a question -- I don't have the impression that he has any mental health problems," Ancelotti said.
"I see him as happy to be here, if he is, he doesn't show it, but I think speculating about problems of this type is a bit ugly."
The forward was left out of France's squad for recent Nations League matches for the second time in two months, and was linked to a rape investigation in Sweden, which Mbappe has denied.
France coach Didier Deschamps did not select the 25-year-old for matches against Israel and Italy, saying "it was better that way".
Ancelotti said he was confident Mbappe, who joined Madrid this summer at the end of his PSG deal, would find the net at the weekend away at minnows Leganes.
"There are always bad moments, all the great strikers have been through them, but he's motivated and happy, and that's all I can see," continued Ancelotti.
"I'm convinced that he's going to play a great match tomorrow and that all this will come to an end.
"He has extraordinary qualities, it's just a matter of time."
