Giroud scored all four goals as Chelsea won 4-0 in Spain for their latest Champions League group clash.
Afterwards, Carlos confessed: "Giroud has done very well, but we have to lift our heads. Our goal has been reached and it was to be in the last 16.
"This defeat shows that we will have to improve things in many aspects. They cannot score four goals like that.
"We have players with many qualities, but things have happened in defence that cannot happen.
"We have an important game this Saturday and we have to improve to do well. We will work with our heads raised."