Chelsea manager Jose Mourinho has stated that he cannot question Diego Costa's commitment levels.

Chelsea have struggled so far this season and arguably one of the main reasons behind the Blues' difficult run is due to the poor form of star striker Costa.

Costa's lack of goals as well as disagreements with Mourinho has led to the striker being dropped recently and there were even reports that the Spanish international could be sold by the Premier League champions in January.

Despite the rumours, Costa was given a chance during Chelsea's 2-0 Champions League victory over Porto on Wednesday night and the former Atletico Madrid ace acquitted himself very well with a quality performance.

Following the game, Mourinho was left very pleased with Costa's display and has stated that he cannot fault the 27-year-old for lack of commitment.

Mourinho told Chelsea's official website: "It's clear but what is also clear is his effort, commitment and great movement, which is something he hasn't had in the last couple of months.

"Tonight it was great. The first goal was obviously an own goal but his movement was great when the pass arrived. Last season he would have scored immediately but this season he couldn't.

"With the second chance when he faced the keeper on his own, you could immediately feel the lack of confidence because the first thing he did was not attack the goal but look to the linesman. When he did that he lost an important second and his last touch on the ball was not the best.

"He could have scored two or three goals today. There is a lack of confidence, clearly, but his attitude was very good and his movement was much better, so goals are coming. I took him off not because I was unhappy with his performance but to give something different to the team, to attack the spaces with faster people."