For more than four years, the two players played together at Stamford Bridge, winning numerous trophies including the Premier League and Europa League.
Mikel currently plays in Turkey with Trabzonspor while Hazard earned a big-money move to Real Madrid this summer.
Hazard spent seven years at Chelsea after joining from French side Lille in the summer of 2012, winning two Premier League titles, two Europa League trophies, one FA Cup and one League Cup.
The Belgium captain is widely regarded as one of the best players in world football but his work ethic has often been called into action.
"The laziest player I have played alongside is Eden Hazard," Mikel told beIN Sports in Turkey.
"Hazard has an incredible talent, 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."
Hazard has not had the best of starts to his Real Madrid career but he was on target twice for Belgium against Russia at the weekend.
Mikel Obi spent more than a decade at Chelsea after controversially joining from Norwegian club Lyn Oslo as a 19-year-old in the summer of 2006.
The Nigerian won two Premier League titles, the Champions League and the Europa League with the Blues.
