After two goals from Samuel Eto'o and a third from Demba Ba saw Chelsea enhance their position at the top of Champions League Group E, Mourinho declined to disclose the full reasons for Hazard's absence.
The Blues boss revealed the Belgium forward missed a crucial training session but was reluctant to comment further.
"Willian played fantastic," said Mourinho, when first asked about Hazard, before being pressed over whether the Belgian was injured.
"I don't want to lie. He's not injured. He forgot the time.
"Let's end the story. He's a kid, kids make mistakes and fathers they have to be clever in the way they educate their sons.
"He didn't play, he wanted to play. He's sad because he wanted to play.
"We won without him and Saturday he's back. End of story."
Mourinho made six changes from the loss at Newcastle, one enforced, with Eto'o replacing the injured Fernando Torres.
Torres, who scored twice in Gelsenkirchen, faces an absence of around three weeks with an adductor injury, but Eto'o and Ba stepped up in the Spain striker's absence.
The Cameroon striker, who dispossessed Cardiff goalkeeper David Marshall as he bounced the ball last month to set up Hazard, ran at Timo Hildebrand as the Schalke stopper prepared to fire down field. Instead Hildebrand kicked it against the striker and saw the ball go into his own net.
There was nothing lucky about the second as Eto'o, previously a Champions League winner with Barcelona and Mourinho's Inter Milan, converted clinically.
Mourinho said: "My favourite players are the players that win matches for me, not the ones that lose matches for me.
"Samuel worked with me in the best season of my career (at Inter). We won everything. So he's in a good position."
Eto'o has started life slowly at Chelsea - they were his second and third goals after his first versus Cardiff - following his move from Anzhi Makhachkala.
Mourinho added: "He was for two years playing without big motivations and when you play without big motivations, you train without big motivations and you lose condition, and you lose sharpness, and you lose even appetite.
"It was not a surprise for me that he arrived here not in the best conditions after two years in Anzhi.
"Now step by step he is going. He is 32 but he's a fit, slim guy.
"He's not a heavy body. He's intelligent, of course, and I think goals give confidence."
Chelsea are now well-placed in the group, three points clear ahead of games at Basle and at home to Steaua Bucharest.
"We won in quite a comfortable way and it's good for us," Mourinho added.
"After the Basle defeat we put ourselves in a difficult situation and it's fantastic that after the fourth fixture we have qualified, almost. Not yet."