London: Jose Mourinho has warned his Chelsea stars they cannot afford any more careless lapses in concentration when they face title rivals Arsenal on Monday.
Mourinho is growing increasingly vexed by the misfiring form of Chelsea's strikers and his defenders' alarming habit of switching off at key moments.
The Blues boss has so far been unable to find solutions to problems that threaten to wreck Chelsea's challenge for the Premier League crown.
Fernando Torres, Samuel Eto'o and Demba Ba have scored just five league goals between them this term, while Mourinho has chopped and changed in an unsuccessful bid to find his best back-four.
Chelsea dropped to fourth place in the table on Saturday, three points adrift of new leaders Liverpool and one behind third placed Arsenal.
And, with so much at stake when Chelsea visit the Emirates Stadium for the final top-flight match before Christmas, Mourinho has made it clear he won't tolerate more sloppiness from his players.
"If we cannot improve our efficiency in front of the goal, we have to improve in the other end," Mourinho said.
"We have to improve when we lose possession of the ball. That's obvious.
"We cannot just let the players hide behind the fact that we are not scoring enough goals and wait for that to happen.
"We cannot play for that. People need to change their brains a little bit more.
"To be a team to play very good football is an important step. To be a team that plays very good football and wins lots of matches is a more difficult step.
"Some players that are used to playing with the ball at their feet and are very comfortable in the offensive phase.
"When the team loses the ball, they have to be also very comfortable working a lot for the team."
While Mourinho battles to cure Chelsea's various ailments, Arsenal manager Arsene Wenger may never get a better chance to finally beat his old rival.
Wenger has failed to defeat Mourinho in nine previous attempts, including a 2-0 loss in the League Cup earlier this season.
In the past, Mourinho has infuriated Wenger with some of his jibes, including calling him a "voyeur"
But, whatever the result, Wenger insists there is no longer any hostility between the two managers.
"It is not a personal battle," Wenger said. "Honestly, we had some big games in the past, but what is important for me is that I am completely focused on Arsenal Football Club and on my team and doing well in the team.
"Once you are out of competition, everybody is different.
"We spent time together in Geneva at the UEFA managers' meeting.
"Here is competition time, so everybody fights for his team and his club.
"Whether we play Monday against Chelsea or anybody else, for me it is exactly the same, because what is at stake for us is to get back to winning habits, whether it is Chelsea or anyone else."
Wenger will be without England midfielder Jack Wilshere, who is serving a two-match ban for an abusive gesture at Manchester City fans last weekend, while French defender Laurent Koscielny is also set to be sidelined with a knee injury.
Wilshere's petulant reaction to Arsenal's 6-3 thrashing at Eastlands summed up the team's disbelief at a loss which raised questions about their ability to maintain their surprise title challenge.
A victory would ensure Arsenal head into the busy Christmas programme back on top of the table, but Wenger has slipped up too many times against Chelsea in the past to take anything for granted.
"Chelsea are a good side with many good promising players, many good young players," Wenger said.
"They have a good offensive potential as well and for us it will be important to have a good defensive focus to find our defensive stability again and to stop them going forward."