However, Bilic's side are undefeated in their last three games, and the Croat has urged his side to maintain momentum in the League Cup.
"We have seven points from three games in the league, so the confidence is back now. We have to continue in this way," Bilic told reporters.
"It's not Wednesday-Saturday, we play Everton on Sunday. So we are going to play a very strong team and try and get through.
"If you go through, because some big teams will have left, you may have an easier game and then you're nearly there."
Chelsea will arrive at the Olympic Stadium high on confidence after back-to-back league wins over English champions Leicester City and Manchester United, and Bilic said he expects a fiercely competitive London derby.
"Chelsea are one of the candidates to win the league and they have quality in all parts of the pitch. They're big opponents," Bilic added.
"Chelsea changed system and they have had some good wins and performances. They are very positive now and playing good football.
"It's a one-off London derby cup game. Five or 10 years ago clubs weren't so keen on this cup but now it's important."
Following recent crowd trouble at the Olympic Stadium, West Ham have announced restrictions on alcohol sales and a post-match segregation between home and away supporters will be in place.
(Reporting by Nivedita Shankar in Bengaluru, editing by Pritha Sarkar)
