English clubs were well below par in the opening round of Champions League fixtures two weeks ago.

Of the four Premier League clubs in Europe's elite, only Chelsea managed to win with Arsenal, Manchester United and Manchester City all coming up short.

Last season, English clubs were finished by the Round of 16 stage of the competition, indicating that perhaps the increased rigours of playing weekly in the Premier League now takes a further toll when competing in Europe.

But Arsenal boss Arsene Wenger says it is too hard to put a finger on the reason why clubs form the UK have not performed as well as they would have liked in recent times on the continent.

"The Premier League is very, very tough. Is that an influence or not? I don't know, but it's a bit early to come to any conclusions. We have to wait a little bit longer," said Wenger ahead of his side's vital clash with Olympiakos at home on Tuesday night.

"A second year without us being successful and you could come to a conclusion of, 'yes, there is something we have to analyse deeply', but I don't believe so at the moment.

"Are we far away? I don't think so, but we have to show that with our performance."