Sunderland manager Sam Allardyce admits his side's defensive frailties are becoming a real concern after their defeat to Everton.
The visitors found themselves two goals down at Goodison Park on Saturday but clawed their way back to 2-2 thanks to Jermain Defoe and Steven Fletcher.
However, three goals in seven second-half minutes left Sunderland facing a mountain to climb before Arouna Kone scored his third of the match in the closing stages to seal a 6-2 victory.
And Allardyce accepts that problems at the back could prove fatal to his side's hopes of avoiding relegation from the Premier League this season.
"The defensive frailties were just too much in the side today and we allowed Everton to win the game comfortably in the end," he said afterwards.
"If we don’t sort those out, and we are going to give it away like we did when we got to 2-2 today, it will be a long haul over the next few months or so.
"We'll have to have a look into it. We've not played too bad in the first half.
"We got back to 2-2 but we just made it so easy for Everton to score three in seven minutes.
"From an attacking point of view we've got at Everton's back players and produced an awful lot of shots at their goal, but out of possession to let them score six from eight shots on target shows the frailties we've got."
Sunderland remain second from bottom in the table after 11 games and could be overtaken by Aston Villa should they beat Tottenham on Monday.
