Fulham boss Felix Magath says his side suffered against rivals Chelsea due to the loss of captain Brede Hangeland.
The Whites were beaten 3-1 at Craven Cottage in the west London derby, with Hangeland the first-half casualty of an accidental clash of heads with Kieran Richardson.
Magath said: "I was satisfied with the first half. We had control of the game and did not give Chelsea many chances, and we had two or three good situations.
"But I don't know what happened - at half-time the players forgot how to defend.
"It was a big problem that captain Brede Hangeland was injured. I don't know how injured he is as he has gone to the hospital. We will just have to wait and see.
"I will remind my players every day in training next week to defend. We will do more defensive work but I hope Hangeland will be back. But we have to work on defending.
“I have seldom seen such a goal we conceded today. (Andre) Schurrle takes the ball and runs over the whole field and no one tackled him. He ran 90 metres without any contact, I have never seen this before.
"When you take over a team that has no wins and losing confidence then you lose morale when you go behind.
"Our leader is not there, so it was too difficult a situation at the moment.
"We have to work on the defence. We have not played like a relegation team in those first 45 minutes."