However, Mikel - who is in London for Nigeria's friendly with England on Saturday - has claimed that Chelsea remain in "very safe hands".
At a press conference, the 31-year-old told reporters: "This club always bounces back, we always bounce back. I am sure Roman knows exactly what to do. Roman and Marina [Granovskaia], I am sure they know exactly what they are doing.
"I don't think the fans should be concerned at all about what is going on. I think it will sort itself out. The club is in very safe hands, the fans should not worry at all."
In over a decade with Chelsea, Mikel made 374 appearances in all competitions.