Fulham boss Rene Meulensteen was left disappointed with their defending for defeat to Sunderland.
Meulensteen admitted Fulham will not drag themselves out of their relegation fight if they keep leaking goals.
Fulham have now conceded 46 goals in 21 league matches, more than any other side.
"You just can't make progress doing that, not at all," he said.
"We were quite in control early on and then we didn't convert those chances, from (Dimitar) Berbatov and (Adel) Taarabt.
"We gave ourselves a mountain to climb.
"These are the games you need to win; simple.
"Their third goal was the defining moment, and credit to them for that.
"We've got to get conceding those goals out of our system."