And the skipper returns in the nick of time because his fellow defender David Luiz will miss the game.
The Brazilian will sit out the match with a muscle injury but it is hoped he will be fit to face Galatasaray in the Champions League on Wednesday.
Mourinho said: "'If, one day, we don't have David Luiz and John the situation is more difficult. John being ready keeps our balance.
"The captain's armband doesn't mean so much, it's a voice on pitch. To have a player to transmit what I need is important.
"John has a level of performance that gives stability to the team, especially one with lots of young people."
The Chelsea boss says he knows the leaders will have their work cut out against sixth-placed Everton but is hopeful his side can claim a vital three points.
Mourinho wary of Everton
'"If we can beat Everton, it is a good weekend for us," said Mourinho. "If we lose points at home, it's never good.
"It doesn't matter what happened in the past. We think we can beat them because we believe in ourselves.
"Everton are a good team, they defend well and are dangerous on the counter-attack. It's a team with good balance.
"They are a very good team, playing very well and getting good results. They're in a position that reflects their quality."