Arsenal manager Arsene Wenger said on Tuesday his side remain in the race for a top-four Premier League finish despite the recent slump in form and will look to ensure a positive end to the season. The North London side, who are sixth in the league and trail fourth-placed Manchester City by seven points, will seek their first victory in four games when they host 14th-placed West Ham United on Wednesday. Arsenal have never finished outside top-four under Wenger, who sees increased importance in finishing with one of the four Champions League qualification spots this season. "It's a good challenge but I think it's certainly possible," Wenger told a news conference. "For 20 years I have done it and it looked nothing. Suddenly now it's important and people realise it is not as easy as it looked. "We are fighting to have a positive end of season. That's why you want the fans to stand behind the team." Wenger said defender Laurent Koscielny, who was substituted at half-time during 2-2 draw with Man City on Sunday, suffered an Achilles injury and is set to have a scan later on Tuesday. "It (the injury) is serious," said Wenger. "If he has ruptured the fibres then he could be out for a few weeks, if not, he could be available to face Crystal Palace. I will tell you more tomorrow." Defender Per Mertesacker and midfielders Alex Oxlade-Chamberlain and Aaron Ramsey return from injury layoff and could feature against West Ham. Arsenal suffered their first home defeat by West Ham in eight years when Slaven Bilic's side won 2-0 at the Emirates last season. (For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports.)