The Frenchman explained that Mourinho's remarkable exit on September 20 left the side in a state of disarray.
However, Avram Grant's arrival has seen the agreement alter - with the Israeli utilising him in all five of his games in charge.
"When I extended my contract last summer, I had an agreement with Mourinho - he would play me for the most important matches but not every three days," he told L'Equipe.
"His departure has messed everything up. The team was suddenly left to itself.
"Coach Grant needed my experience, that's why he has played me often.
"Mourinho has created stability for three years. His departure has destabilised most of the players, especially the youngsters.
"It was very difficult. We had to be self-managing to rediscover Chelsea's fighting spirit - we had lost that a little."