Hiddink had a caretaker spell in charge of the Blues in 2009 after Brazilian Luiz Felipe Scolari departed.
"We have moved on and the atmosphere has improved since the change of manager," Mikel told British media. "Jose is a fantastic manager, but sometimes football is a cruel game and you have to move on.
"He came back to the club a second time and won two trophies but now he is gone. Is it the right decision? We will only see in the future."
The Nigerian is one of few players, along with defenders John Terry and Branislav Ivanovic, who were at the club during Hiddink's previous period in charge, when the Dutch manager led them to an FA Cup win.
"He (Hiddink) hasn't changed much yet, but he was here before and he knows the place and all the staff," Mikel said.
"We are down there in the table for a reason so he can not come in and perform miracles.
"We have had three games now without losing, so (we) are making the right steps."
Mikel, who got limited game-time under Mourinho making just two starts in five league appearances, could not explain Chelsea's meek title defence this season.
"It is difficult when you are not playing, as you do not really know what the problems are," Mikel added.
"I was not playing that much under Mourinho. It was a collective thing - the players and the manager were not performing."
Chelsea, currently 14th in the table with 20 points, travel to Crystal Palace on Sunday, hoping to register their first win under Hiddink. Palace are fifth, having gone six games without defeat.
(Reporting by Nayan Das in Bengaluru; editing by Amlan Chakraborty)
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