Hazard, 30, has been widely criticised for failing to replicate his scintillating Chelsea form at Real Madrid since his stunning move in 2019.
The Belgian winger has been plagued with injures during his time at the Spanish club, with uncertainty continuing to mount over Hazard's Madrid future.
Former Chelsea boss Mourinho recently praised Hazard as an "amazing kid" and "amazing player."
However, the 58-year-old Portuguese manager claimed Hazard was "awful" with training and suggested he would be "much better" if he maintained high fitness levels and conditioning.
Mourinho told talkSPORT: "The truth is that amazing player that you see is an amazing player with awful training. You can imagine what he could be with a super-professional attitude in training.
"In the end, he is an amazing kid, he is an incredible family man. He looks like he doesn't belong to this generation of players, he's very quiet, he's totally focussed on family, on kids, on parents, on a very quiet life.
"But he gets onto the pitch every morning and he doesn't work much. When he goes onto the pitch, you don't see the reflection of a week's work, you just see the reflection of his talent.
"So he is this amazing player, and you can imagine if he was a top professional. But in terms of his fitness, his speed, his condition, he would be a much better player [if he trained harder]."
Fabregas, 34, lifted two Premier League titles when he played alongside Hazard at Chelsea.
The former Arsenal and Chelsea star suggested that Mourinho's criticism of Hazard could be right due to his approach in training.
However, Fabregas claimed that it would be unfair to compare the Madrid flop to Lionel Messi and Cristiano Ronaldo, who are "different animals."
The Monaco star told The Daily Telegraph: "I saw that Jose Mourinho was recently critical of his training and is it true that sometimes maybe he seems like he doesn't care in training or doesn't approach training the way he should?
"Probably, yes, but it is not really fair to judge him against two players like Cristiano and Leo, who are different animals.
"You also have to remember that Eden has broken his ankle three times and the moment when he moved to Real Madrid and I felt it was time for him to explode and do something really special, the luck didn't go in his favour.
"Unfortunately, you cannot control when you have the ball and someone comes up behind you and kicks you, and this has been happening to Eden even before I started playing with him.
"Jose was always complaining that Eden was getting kicked and wasn't getting any protection and now, unfortunately, we have seen the result of that.
"He's a very strong player, he keeps taking the ball, getting kicked, getting back up, continuing to play and because of this the defenders have to kick him harder and harder to keep him down."
Featured Image Credit: PA
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