Referee Tom Henning Ovrebo has admitted making mistakes in Chelsea's Champions League semi-final against Barcelona in 2009.
The match finished 1-1 with an Andres Iniesta equaliser sending Barcelona to the final on away goals after a scoreless first tie at the Nou Camp.
The Norwegian official turned down four Chelsea penalty appeals on the night, the most contentious a Dani Alves foul on Florent Malouda in the penalty area which resulted in a free-kick outside the box, rather than a spot-kick.
Ovrebo told Marca: "It was not my best day really. Some days you are not at the level you should be. I can't be proud of that performance.
"There were several errors and everyone will have their opinion of those plays."
Chelsea, who face Manchester United on Sunday live on Sky Sports Premier League, were also aggrieved that Ovrebo turned down penalty appeals for handball against Samuel Eto'o and Gerard Pique.
"They were handball situations. I judge them on the pitch and I think it is interesting to know what I think of those actions once judged, although I understand that people think different to the decisions I made at the time," said Ovrebo
At the final whistle, Ovrebo was surrounded by angry Chelsea players with Didier Drogba and Jose Boswinga subsequently banned by UEFA for their behaviour.
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Ovrebo said that he received death threats from Chelsea fans, and had to change hotels after the game
His comments come ahead of Chelsea and Barcelona's round-of-16 first leg at Stamford Bridge on Tuesday.