Theo Walcott (R) and Robin van Persie of Arsenal attend a training session ahead of their UEFA Champions League Group F match against Olympique de Marseille at London Colney on October 18, 2011 in St Albans, England.

Olympique Marseille and Arsenal look to put their mediocre domestic form behind them as they gear up for a potentially decisive Champions League clash at the Stade Velodrome on Wednesday.

Marseille, the 1993 champions, have won only one Ligue 1 game this season although they lead Champions League Group F with six points from two games, having crushed Borussia Dortmund 3-0 in their previous match.

Arsenal, who have yet to win the Champions League, are second on four points in the group and lie 10th in the Premier League standings having had trouble adjusting after Samir Nasri and Cesc Fabregas left during the off-season.

Victory would give Marseille a perfect record midway through the group phase. Didier Deschamps's side, however, will need to improve dramatically from their dull Ligue 1 displays if they are to challenge the Londoners.

Marseille, 15th in the French league, drew 0-0 at Toulouse at the weekend and have not won a league match in almost a month.

"I don't want to be too pessimistic (about our situation)," Deschamps told the club's website (www.om.net). "I'm aware of the difficulties we are facing but we are working on that and we are trying to build some confidence."

Arsenal can empathise with their rivals' predicament.

"Marseille is a good team but they are under pressure a little bit like we are in the league because they didn't start as strong as they would have expected," said Arsenal coach Arsene Wenger.

"That puts more pressure on you. They have done well in the Champions League, certainly, because it is a competition where there is a bit less expectation and they are less under pressure."