Very bad night
The Hammers headed into the clash at the London Stadium, looking to have another excellent cup journey similar to the previous season.
However their journey was ended in embarrassment, with goals from Yaya Toure, Havard Nordtveit, David Silva, Sergio Aguero and John Stones and Bilic admitted that the performances was poor.
"Of course it’s a bad defeat for us," Bilic told whufc.com. "We started well but in the space of 15 minutes after the first goal."
"When we had the chance to equalise we made a mistake," he sated. "They had enough quality to use the space behind and in between the lines."
“Tonight’s result was fair and it was very hard for us to find any consolation," the coach admitted. "For half an hour, it was good for both sides."
"It was a very bad tonight at the end," Bilic added. “As a team, it was not good enough and nowhere near the performance we had here a few days ago against Manchester United."
Getting the confidence back
West Ham will be looking to dust themselves off on Saturday afternoon, when they welcome former manager Sam Allardyce to Stratford with his Crystal Palace side.
This is one of two crucial games for Bilic's side in the next few weeks, with a trip to Middlesbrough the week after and Bilic stated that his side will work to get their confidence back.
"Always when you have a big defeat, it affects the confidence,” he continued. “The game against Palace though, we have enough days to work and get the confidence back and be ready against Palace."
"But in the game before," Bilic stated. "Some players played really well last time with ten men [against Manchester United]."
"They showed that we can defend well as a team," he concluded. "It showed we do have quality in the team.”
West Ham United will take on Crystal Palace at the London Stadium on Saturday, January 14 with kick-off at 3pm GMT.