Arsenal star Per Mertesacker revealed that it would be difficult to progress into the latter stages of the Champions League following their loss to Olympiacos, Express reports.
The 31-year-old came on for the final 33 minutes after teammate Laurent Koscielny picked up a hamstring injury in the 3-2 home defeat.
This is their second consecutive loss in the group stages after they fell to a 2-1 defeat to Dinamo Zagreb two weeks ago.
Mertesacker admitted that despite their good start to the match, they failed to keep their discipline and will now face a tough task trying to continue their run in the tournament.
“First of all, we are disappointed because we started quite well, especially on the break after they had set-pieces,” he said.
“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.
“If we are not disciplined and do not chase the ball we have got no chance.”
The Gunners will have to put their recent loss behind them as they now have to prepare themselves for the upcoming clash against Premier League leaders Manchester United at the weekend.
Manager Arsene Wenger needs to keep his team’s confidence up given that they travel to Watford the following weekend before continuing their Champions League campaign against Bayern Munich.