The Blues were beaten 3-0 at Arsenal on Saturday which was their second defeat in a row, extending their winless streak to three in the Premier League.
"There are no excuses," the Belgian playmaker told the club's official website.
"It was not good. We lost too many duels.
"We came to win the match but we made mistakes, for the first goal, another for the second and then before we knew it we were already 3-0 down.
"Every weekend at the moment we having to come back and score. We did it at Leicester (in the EFL Cup) but against Arsenal, who were playing at home, it was not possible.
"They played well. We need to be better. In the last three games in the league there have been nine points available and we have got one. It is disappointing.
"We need to go away and work on what we are doing wrong ahead of the big matches that are coming up."