Novak Djokovic has admitted that he was embarrassed by his performance following the 6-3 6-1 defeat to David Ferrer at the ATP World Tour Finals in London.
A sensational season is in danger of ending in disappointment for the Serbian, with his place in the semi-finals dependant on the results of his match with Janko Tipsarevic and Ferrer's clash with Tomas Berdych on Friday.
"All credit to my opponent, he played a great match," the Serbian told Sky Sports News.
"But I just wasn't there. It was the worst match I've ever played this season so far definitely. So many unforced errors. I'm not playing well. That's a fact."
Djokovic has lost just five of his 75 matches this season but could miss out on a spot in the semi-finals.
