Chelsea boss Mauricio Pochettino admits he is "worried" by France forward Christopher Nkunku's latest injury setback.

Nkunku has missed Chelsea's last two games with a hip problem after being sidelined for much of the season due to a knee injury.

The 26-year-old has made only one Premier League start since his close-season move from Leipzig and Pochettino conceded on Friday that the latest setback is "complicated".

"I am worried about the situation of Nkunku. (It has been) now 10 days that he can't train. We're assessing him," Pochettino told reporters ahead of Saturday's London derby against Fulham.

"He suffered a small issue and it became complicated. After six months that we were waiting for him, he was so close to feeling comfortable.

"We're disappointed. We want him as soon as possible."

Nkunku was made to wait until December for his first start following a prolonged recovery from his pre-season knee problem.

He scored on his top-flight debut in the 2-1 defeat at Wolves on Christmas Eve and he made his full debut three days later against Crystal Palace.

Nkunku's fresh absence places further pressure on Pochettino's limited attacking options, with Nicolas Jackson on Africa Cup of Nations duty for Senegal at present.

Pochettino urged Chelsea to beat Fulham this weekend to erase the frustration from Tuesday's shock defeat at second tier Middlesbrough in the first leg of the League Cup semi-finals.

"It's true that after the first 90 minutes we are 1-0 down. We need to keep the belief, the team is preparing well. I'm so sure we'll do a good job," Pochettino said.

"But when you lose a game to a Championship team, you need to accept the criticism. We have the chance on Saturday to put all these bad feelings out by performing in the right way."