Just two minutes after Hazard was taken off, Jesse Lingard scored the decisive goal past Courtois to give Manchester United the three points.
"After our goal, we conceded a counter-attacking goal just like last Tuesday but in the second half we had less of the ball, but even then we should never have lost this match," he said.
"I have no explanation for the sub of Hazard. I had not expected him to take him off but it is a choice of the manager. He must explain. I can't look into his head.
"Players like Eden should have 90 minutes on the pitch. He can always bring something extra offensive."
These comments come as Conte finds himself under increasing pressure at Chelsea, and Courtois himself has been heavily linked to Real Madrid.