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Matches: Arsenal vs. Montpellier and Schalke vs. Olympiakos, Group B, Wednesday at 2:45 p.m. ET
The top of Group B is a three-car pileup waiting to happen.
German club Schalke lead the group with eight points through four matches after beating Arsenal in London on Matchday 3.
Arsenal are second with seven points, and Olympiakos are third with six. The top two teams advance to the knockout stage.
Schalke can seal qualification by beating Olympiakos on Wednesday. If that happens, Arsenal could also qualify with a home win over Montpellier, who have already been eliminated.
But considering the way Arsenal's season has played out so far, the easiest scenario also feels like the least likely.
Two weekends ago, the Gunners blew a two-goal lead against Fulham before eventually drawing 3-3. On Matchday 4 in the Champions League, they led 2-0 at Schalke before drawing 2-2.
But this past weekend, Arsene Wenger's team fell behind North London rivals Tottenham Hotspur before eventually winning 5-2.
Such erratic results suggest anything could happen Wednesday—and on the final matchday. Forward Olivier Giroud has started to round into form, but the Gunners defense has been poor lately.
How will they fare this week?