Arsenal defender Per Mertesacker has stated that there are no excuses for the Champions League defeat to Olympiacos on Tuesday evening.

The Gunners have now lost their opening two games of the group stage after the Greek side left the Emirates Stadium with a 3-2 victory.

Mertesacker has said that the performance was well below the standard expected of an Arsenal team.

"First of all, we are disappointed because we started quite well, especially on the break after they had set pieces," he told the club's official website.

"We lacked that concentration and it is not understandable why we drifted and did not do the job we are used to doing. That is not acceptable and we will be punished [for that] in the Champions League.

"We need to get behind the ball and play better defensively. We lacked discipline, even when you get a goal back don't rush yourself. Get your discipline back and with possession you get your chances. If we are not disciplined and do not chase the ball we have got no chance."

Arsenal return to Premier League action on Sunday when they host Manchester United.