Nemanja Matic has voiced his frustration with Chelsea's lack of consistency this campaign.
The reigning Premier League champions have been in dismal form this season and are mired in 16th place following their 2-1 defeat at Leicester City on Monday.
Chelsea have done significantly better in the Champions League, though, beating Porto last week to clinch top spot in their group and a place in the last 16, and Matic cannot explain their inability to reproduce that form domestically.
"I cannot explain why consistency has been so difficult to achieve," Matic told the official Chelsea website.
"I don't know what happened to us against Leicester. In the game against Porto, a very good team, we played very well, we scored two goals and created chances, but we were like another team on the pitch against Leicester.
"It is one more game that was not good for us. We are sad because of the defeat but we have to keep going, to try to win some games and to recover from this situation which is not easy for us. We have to try to be better than we were."
Chelsea were paired with Paris Saint-Germain during Monday's draw for the Champions League round of 16 and Matic expects a tight tie.
"It's going to be a great experience for us, two great games, very hard I have to say, but in these kinds of games you don't have favourites – anyone can go through," he added.
"I am sure that it's going to be interesting and I hope we can do something."
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