"His work [in training] is reflected in the games. He is scoring a lot of goals for us," said the full-back on Chelseafc.com.
"He works very hard for the team, he makes a lot of movement and he is a big part of our team.
"We are happy he is scoring goals, because if he is scoring goals it seems we are doing the right thing and he is getting the chance to score."
Costa has now scored four goals in as many Premier League appearances so far this season.