Already well off the pace in the Premier League, Arsenal could also find itself in trouble in the Champions League if Schalke beats the English team for the second time in two weeks on Tuesday.

Arsenal's miserable recent run of form included a 2-0 loss to Schalke at Emirates Stadium, leaving the German side top of Group B after three games.

If Arsene Wenger's men lose again at the Veltins-Arena, they could be level on six points with Olympiakos and facing a battle to secure the second qualification spot and a place in the knockout stage for the 13th straight year.

''We have to bounce back. I think we have to show how much we want to win it and go there and show big attitude,'' said Arsenal midfielder Mikel Arteta. ''I have no doubt about the attitude that we have in the dressing room, and the desire.''

The lackluster 2-1 loss at Manchester United on Saturday, in which the score barely did justice to the hosts' dominance at Old Trafford, has hardly improved the mood among Arsenal fans, who vented their anger at the club's hierarchy throughout the match. The result left Arsenal nine points off new leader United.

Olympiakos hosts Montpellier, which is bottom of the group on one point, as the Greek team looks to close the gap on the front-runners.

Schalke ended Arsenal's 45-game unbeaten home run against foreign visitors by outplaying Wenger's side two weeks ago. Klaas-Jan Huntelaar and Ibrahim Afellay, the scorers that night, will be licking their lips after seeing Arsenal's defensive struggles continue at United.

The most-criticized member of the defense was left back Andre Santos, who has been an accident waiting to happen in recent games and was given the runaround by winger Jefferson Farfan against Schalke. Santos, a Brazilian who seems more at home going forward than defending, was also slated for asking for former Arsenal striker Robin van Persie's shirt at halftime but should keep his place because Kieran Gibbs is still out with a thigh injury.

While Aaron Ramsey has been ruled out with a groin strain, fellow midfielder Jack Wilshere is available for a Champions League fixture for the first time since March 2011. Arsenal has the forwards to worry Schalke, whose five-game winning run across all competitions came to an end Saturday with a 3-2 loss at Hoffenheim in the Bundesliga.

''It is good that we now have another game so soon, so that we don't have long to think about this game,'' Schalke defender Benedikt Howedes said. ''Arsenal are a great team and we are going to have to keep our concentration high.''

Schalke, which has lost only two of its past 12 Champions League games in Gelsenkirchen, is without defender Christoph Metzelder (groin), while midfielder Marco Hoeger is struggling with a left ankle injury.