The league's top scorer sat out the team's draw with Schalke in the Champions League earlier this week with a hamstring problem.
Read below what else the manager said in his weekly press briefing:
12.18pmHello! We'll be hearing from Chelsea manager Jose Mourinho in the next 15 minutes ahead of the league leaders' trip to Manchester City this weekend. The match comes just four days after the Stamford Bridge side were held to a 1-1 draw by Schalke in the Champions League.
12.20pmThe Blues have looked imperious in the Premier League so far, winning all four of their matches by at least two goals. They also boast the league's top goal-scorer in Diego Costa, who has netted seven times so far this season.
12.23pmThere is a fitness concern over the Spaniard though, as he missed their Champions League match earlier this week because of a hamstring injury. Mourinho recently revealed that the injury is restricting Costa to just one match per week.
12.26pmChelsea have a busy couple of weeks coming up. After this match, they'll face Bolton in the League Cup, before hosting in-form Aston Villa in the league, ahead of a trip to Sporting Lisbon.
12.29pmAs with all Premier League matches, Sports Mole will have live coverage from the match, as well as team news ahead of kickoff, manager reaction and player ratings from this match on Sunday.
12.32pmMourinho is now in the press centre ready to speak to reporters, so let's see what he has to say...
12.33pmWhen asked about the added significance of facing a title rival, Mourinho says: "It's one more game and three more points but when matches are between title contenders, every point makes a difference."
12.35pmOn the prospect of a trip of the Etihad, Mourinho admits that he has been doing his research: "We know what it's like to win there and lose there. I watched last season's games to identify the differences."
12.38pmTurning his attention to his squad, Mourinho reveals that Costa would be ready to play on Sunday: "Everybody is ready to play, Diego is not in the best condition but he will start. If he plays he won't play against Bolton. I don't want to compare squads but ours is better than it was last season, we have more solutions. We have a good balance."
12.41pmChelsea could face a former player in Frank Lampard this weekend, but Mourinho does not think that it will be weird for him or his players: "No, that's football, maybe if you asked me three years ago, or few months, yes. When he signed for New York team, I was not expecting that. He has my respect."
12.44pmOn the subject as this weekend's opponents, Mourinho says that he respects the Premier League champions, but that his players are confident: "It's always a good time to play against big teams because it makes my job easy. We respect City totally because they deserve it, but we believe in ourselves. The perfect situation is to score a lot of goals and not concede, and we have to chase that perfection."
12.46pmAnd on that note, Mourinho makes his exit to continue to prepare his squad for their trip to Manchester.
12.49pmSo that's all from this press conference, but join us again later as Louis van Gaal will be talking to the media, and join us again on Sunday to see if Chelsea can maintain their unbeaten start to the season. Thanks for joining me this afternoon, goodbye.