Chelsea boss Maurizio Sarri admits his defence must improve after their derby thriller against Arsenal.
Marcos Alonso produced a late winner as Chelsea defeated the Gunners 3-2.
Sarri said, "We did very well in the last 25 minutes today, but we have to work and improve in the defensive phase, and we are not only talking about the defenders.
"If we want to defend by looking only at the ball, we need to stay very compact and press in the other half. In that 15 minutes, we were not able to do that, and so we were in trouble.
"We need to continue, and press and press and press in the other half, otherwise for us there may be a problem. We will be in trouble in the defensive phase and not able to move the ball like we did in the first 25 minutes.
"I hope in two months we will be able to play for 90 minutes like we did the first 25 minutes."