The north Londoners saw a successful start to the season abruptly halted at the weekend as they fell to a 2-1 defeat to Chelsea at the Emirates Stadium. Arsenal sit seven points shy of the Barclays Premier League leaders as a result, but attention now turns to their European campaign.
Wenger's side takes on the Greek champions in Group B, and the Frenchman said: "The players are focused and disappointed that we lost the game. They are still down of course, but we have a Champions League game in front of us at home and we want to put things right."
He added: "There were a lot of positives in that game as well, what was not good is easy to correct. I believe the championship is long, but we have to make sure the Champions League is long as well.
"It is about how we respond. I am impressed by the mentality of my team, but the mentality is as well about how you respond to disappointment. I am confident we will, but that is what we want to show tomorrow."
Arsenal will be hoping to make it two wins from two Group B games, having returned from Montpellier with three points on matchday one.
Olympiakos, who Arsenal also faced in the group stage last year, are without a point after losing their opener at home to Schalke and Wenger knows Wednesday's clash at the Emirates provides a chance to take a stranglehold on the group.
He said: "Olympiakos are already in a position where their backs are to the wall because they have lost at home and in this Champions League when you lose at home it is very difficult. They are highly motivated to know they have to give everything to make it through."
Wenger, who is still serving a three-game touchline ban, will have to do without several key players. Goalkeeper Wojciech Szczesny's return from an ankle injury is still three weeks away, while midfielder Tomas Rosicky and right-back Bacary Sagna remain sidelined.
Wenger also revealed playmaker Mikel Arteta faces a fitness test on an ankle injury on Wednesday morning, while midfielder Abou Diaby faces a three-week lay-off with a thigh strain that forced him off against Chelsea.