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.