Costa will be available for his side’s Premier League clash on Wednesday even if not fit on Sunday.
The Chelsea boss added Didier Drogba is available but Loic Remy remains a doubt ahead of Premier League title clash.
Dominic Solanke did not play for the Under-21s yesterday and Mourinho added that he will be called upon if needed.
Cesc Fabregas returns to face his former side on Sunday and his manager is not expecting there to be any problems, and has no worries about his midfielder dealing with a possible bad reception.
Mourinho is not focussing upon his impressive record against Arsene Wenger and says it will be an achievement to win at the Emirates.
He hailed the strength of Arsenal’s squad but is confident his team will do enough to win, but was adamant that the Blues have not won anything yet and knows every club has pushed hard in recent weeks.
Mourinho said: “Good projects end with titles. Cesc was looking for that.”