The Stamford Bridge club finished their campaign with a 2-1 victory over relegated Cardiff City on Sunday and Mourinho immediately turned his attention to strengthening his squad for a championship charge next year.
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The victory sees Chelsea finish four points behind champions Manchester City, but Mourinho's side scored 31 fewer Premier League goals - an area of obvious need for improvement.
"Finishing third is not a drama, it is a position we will have to accept in a transitional season," the Portuguese said. "We deserved to win (against Cardiff), we played well, especially for an end-of-season game.
"We need to improve, we know that, but today with young players in creative roles we played well.
"We can improve our killer instincts, because we need to score more goals from less chances.
"The club will not run away from the responsibility of bringing in a couple of important players to help the team immediately."