Chelsea chief executive Peter Kenyon says three players will leave in the summer - but they will not include Shaun Wright-Phillips or Didier Drogba.
The Blues, who retained the Premiership title on Saturday, will make three new signings and Bayern Munich midfielder Michael Ballack is a transfer target.
Kenyon told BBC Radio Five Live: "It will be three in and three out.
"One of those is clearly Michael Ballack and we hope we can get that done before the World Cup."
Bayern director Karl-Heinz Rummenigge thinks Chelsea's move for Ballack, 29, is "set in stone".
And if the German international does move to Stamford Bridge, Kenyon says he will not be the only new face.
"I am convinced that the players we will bring in for next season will move us on as a team"
Kenyon added on Five Live's Sportsweek programme: "There is a constant process of improving the team.
"We have got a 24-man squad and that is what we want to maintain. We think that is right for the competitions we are in. It is right from a rotation point of view.
"We can improve, we need to improve and we will improve but we are talking about improving what is already a fantastic squad - it is not easy.
"I am convinced that the players we will bring in for next season will move us on as a team. The ambition at this club from everybody - the board, the owner and the manager - is to do well domestically but also to win the Champions League."
Kenyon also rubbished reports that Mourinho would leave Chelsea, despite securing the club's second successive League title.
Mourinho said on Saturday: "A couple of times, I thought about closing the door and saying goodbye."
But Kenyon explained: "He wasn't close to leaving at all.
"He is a very emotional guy. What he was saying is he had some thoughts.
"He is someone where things happen and then everybody moves on - and that is what happened. It was never in question, it was never serious.
"He is going to be here next year and I think he is going to be here for many years to come.
"He knows what we want to achieve and he has got the resources here and the support here to do it. We are all 200% behind him.
"To win the Premier League is fantastic but to win it in back-to-back seasons is historical"
"There is no question he thinks he has finished the job he came here to do - and we don't think that. He is young, he has got many years ahead of him, he's got a great future and what better place for him to be.
"When you look at it in the cold light of day, why would you move somewhere else? There is plenty of time for him to consider other parts of his career a long way down the track.
"He is proud of what we are doing here and what he is doing .
"Sometimes I think he cannot understand why we don't get the credit and he does not get the credit he thinks we deserve. I have to say I fully support him in that.
"To win the Premier League is fantastic but to win it in back-to-back seasons is historical. Only one other team has done it since the Premier League started - Manchester United - the team we beat convincingly and with style on Saturday. "