Hazard and Mikel, now of Trabzonspor, shared the Stamford Bridge dressing room for over four seasons.
The Belgium international arrived in 2012 and went on to make 352 appearances for the club, scoring 110 goals.
In June, he completed a coveted €100million move to LaLiga giant Madrid.
Mikel raved about the 28 year-old's undoubted ability but gave a less positive assessment of his work ethic when asked to name the laziest player he trained alongside.
"Hazard has incredible talent," the Nigerian said. "Maybe not as good as [Lionel] Messi, but he can do whatever he wants with the ball at his feet.
"He didn't like to train hard. While we were working he was waiting for us to finish training just standing there. But on Sundays he was always man of the match, it was unbelievable."
Mikel, a Champions League winner with Chelsea, named current Blues boss Frank Lampard the hardest trainer he has seen.