London, Oct 1 (IANS): Chelsea forward Diego Costa has said that loss of confidence may be the reason for the English football champions' recent setbacks.

Currently, Chelsea hold the 14th position in the English Premier League (EPL) standings after the team lost 1-2 against Portuguese outfit FC Porto on Tuesday in the European Champions League second round of the group stage, Efe reported.

"We are all united. It's not a good moment now. We must do more. We have a good squad with a great deal of quality. We have maybe lost some confidence in three or four games," Costa said on Wednesday.

"The manager knows the quality of his team. He knows what we can do. It is the responsibility of all of us," the 26-year-old former Atletico Madrid star added.

The Brazil-born Spanish international felt that they failed to lift their game at critical junctures against Porto.

"We knew it was going to be a physical game. We began well. Things changed when they scored, but we quickly equalized. In the second half the same thing happened -- we were lacking concentration at key moments of the game," Costa explained.