Guus Hiddink has told his Chelsea squad to "look at themselves in the mirror" and be "ultra-critical".
The Dutchman, a short-term replacement for sacked Jose Mourinho, also said he would have a "brief" chat with players who did not have the necessary desire.
Chelsea sit 15th in the Premier League after 17 games, just three points above the drop-zone.
Hiddink added that finishing fourth was still a "mathematical possibility" but said it would be a very difficult task.
"This league is very strong," he said. "All the teams can kill each other."
The former Netherlands coach, 69, also revealed he was keen to bring former striker Didier Drogba back to the club to work alongside him.
Hiddink first managed the Blues on a temporary basis for the final three months of the 2008-09 campaign, replacing Luiz Felipe Scolari.
He helped them win the FA Cup, took them to the semi-finals of the Champions League and steered them to third in the Premier League, seven points behind champions Manchester United.