The Blues' Premier League title hopes were dented Saturday following their 1-0 defeat to Crystal Palace, which left the club two points behind first-place Liverpool after that club's Sunday win over Tottenham.
Samuel Eto'o, Fernando Torres and Demba Ba have scored just 15 league goals this season, and Mourinho believes that some members in his current squad need to improve in order to win the title.
"I can't, and I don't, need to improve [Gary] Cahill, [Branislav] Ivanovic, John Terry. I can't improve them and I don't need to improve them. But there are other guys I need to improve. I think we are doing that step by step but it is not enough to be champions."
Earlier this month, Goal UK reported that Chelsea has taken the first steps to making Atletico Madrid's Diego Costa its headline summer signing and Mourinho says that players will be making way at the end of the season as well.
"The ones that are staying are competing with the striker we are bringing," Mourinho said. "And it is also sometimes normal that, at the end of the season, players — I am not speaking about the strikers — but players that are not playing a lot or are not happy and prefer a change. That is part of the market.
"We want to improve the team and the players and make some surgical movements in the transfer window."