LONDON (Reuters) - Arsenal face Olympiakos Piraeus in the Champions League on Wednesday with manager Arsene Wenger talking nervously about a defence he says lacks personality and authority after they suffered their first defeat of the season.
The north London club will be expected to return to winning ways against the Greek league leaders after they were beaten 2-1 at home by Premier League pacesetters Chelsea on Saturday.
Despite conceding only four league goals in their first six games and winning their opening Champions League encounter 2-1 against Montpellier, Wenger felt the weekend's defensive display in which they conceded twice from set pieces was a cause for concern.
"Defensively we were just not at the level you have to be in," he said about his side's rearguard.
"For the rest, we have shown quality and spirit but we have to show more personality and authority on the goals we conceded."
German defender Per Mertesacker was rested on Saturday and could return as Arsenal face Olympiakos in the group stage of the competition for the third time in four seasons.
The omens are in Arsenal's favour having not lost a European home game in their last 15 while no club from outside England has beaten them in 47 European home matches.
They have also not lost any of their seven home games against Greek clubs.
Olympiakos are currently bringing up the rear of Group B, having lost their opening group match to Schalke 04 2-1, and have a distinctly poor record in England, losing on all 10 previous visits, conceding 31 goals and scoring only twice in those games.
They are, however, blazing a trail domestically having won their opening five matches. They have also developed a knack of nicking away wins, winning their last three European matches on the road by 1-0.
Leonardo Jardim's team were made to work hard for their latest domestic win, beating Atromitos away 1-0 courtesy of David Fuster's first-half strike.
The Spanish midfielder headed in Olympiakos' consolation in their 2-1 defeat at the Emirates last season when Alex Oxlade-Chamberlain marked his Champions League debut with an early goal and Andre Santos scored his first for the club to secure the points.
Olympiakos will be boosted by the return of Algeria striker and the Greek Super League's top scorer Rafik Djebbour, who missed the weekend win, but Greece full-back Vasilis Torosidis is out.
Within the Olympiakos ranks there is a familiar foe for Arsenal in the form of goalkeeper Roy Carroll who played for Manchester United when they ended the Londoners' famous 49-match unbeaten run in 2004.
The Northern Ireland international joined the Greek club in 2012 after a nomadic seven years in which he played for five different clubs including West Ham United and Rangers.
The game in 2004 resulted in a tunnel bust-up that became known as "pizza-gate" or the "battle of the buffet" after a slice of pizza was reportedly thrown at United manager Alex Ferguson after the match.
"That game in 2004 was a great occasion and I was delighted to keep a clean sheet," Carroll said in the Daily Mirror.
"So to beat them and end their unbeaten run was fantastic. I honestly still don't know exactly what happened in the tunnel after the game."
Arsenal: 24-Vito Mannone, 5-Thomas Vermaelen, 28-Kieran Gibbs, 6-Laurent Koscielny, 25-Carl Jenkinson; 19-Santi Cazorla, 15-Alex Oxlade-Chamberlain, 16-Aaron Ramsey, 8-Mikel Arteta; 9-Lukas Podolski, 27-Gervinho
Olympiakos: 42-Balazs Megyeri, 2-Giannis Maniatis, 15-Pablo Contreras, 24-Kostas Manolas, 20-Jose Holebas; 23-Dimitris Siovas, 3-Francois Modesto; 19-David Fuster, 7-Ariel Ibagaza, 5-Paulo Machado; 10-Rafik Djebbour
Referee: Svein Oddvar Moen (Norway)
(Additional reporting by Graham Wood; editing by Justin Palmer)