Chelsea defender Gary Cahill claims he is unaware as to why Antonio Conte's side have struggled in 2018.
The Blues have managed to win only one of the five matches in the Premier League in this calendar year. They have won only two of the last 10 matches in all competitions, which includes a 2-1 aggregate defeat to Arsenal in the two-legged semi-final clash of the Carabao Cup.
Conte saw his side concede seven goals in the last two defeats against Bournemouth and Watford, while Chelsea managed to score only one goal in the process. Cahill started in his side's last two defeats. The series of poor results has seen them drop further down in the league table.
Chelsea are now fourth in the league table with 50 points after 26 games, trailing third place Liverpool by a point. The Premier League winners trail second place Manchester United by six points.
"I don't know. It's very hard to ever criticise our squad in terms of work-rate or commitment, is it a confidence thing? I don't know. For whatever reason, that happened. But that's football as well. It's not like it's the first time it's ever happened in my career," Cahill told Sky Sports.
"You go into games where everything feels OK and all of a sudden things don't go well. Against Watford, we had the sending off early doors, got to 1-1 and then fell apart. People say why, but we don't know why.
"We worked hard and in the end we didn't have enough and quality wise it wasn't there. I had a very bad feeling after that game personally about my performance. You beat yourself up and then move on and get back on track."
Chelsea host West Bromwich Albion in the next tie on 12 February. Cahill wants his side to bounce back when the west London club face Alan Pardew's side at Stamford Bridge.
"The last two results and the performances were not good enough. As players, and I am sure as the manager, the only thing you want is the next game to come around so you can try and put it right and we have that opportunity on Monday," the defender explained.
"I feel this month is very important. I think when we come out of the end of February it could shape the season. We realise that. If we get the right result and performance on Monday you start getting that confidence back into the team and keep building from there."