Laurent Koscielny
Laurent Koscielny has been ruled out of Arsenal's clash against Manchester United on SundayGetty

Arsenal's woes are set to continue into the weekend. If back-to-back defeats in the Champions League against Dinamo Zagreb and Olympiacos are not enough, Laurent Koscielny has now been ruled out for the Gunners' crunch clash against Manchester United on Sunday 4 October. The French international has been one of the best players for the north London club thus far this season, but will now be sidelined with a hamstring injury picked up during their midweek loss against the Greek champions.

According to the Telegraph, the defender will miss the clash against the current Premier League leaders, as he undergoes tests to determine the extent of the injury. It is claimed that he has suffered a hamstring tear, which is likely to see him only return to action following the international break, which commences next week. Koscielny is also expected to miss France's two friendlies against Armenia and Denmark on 9 and 12 October respectively.

This will come as a big blow to Arsene Wenger ahead of their crunch clash against the 20-time English champions, as the former Lorient defender was building a nice understanding with Gabriel at the heart of the Arsenal back four. According to the Daily Mail, the French manager is keen to see the new partnership blossoming, as he views the duo as the future of the Gunners' central defence. Per Mertesacker will deputise in Koscielny's absence, and the former German international has called on the team to respond following their poor performance against Olympiacos in the Champions League on Tuesday (29 September) night.

Meanwhile, the Telegraph report claims that first-team players at the club were surprised to see David Ospina get the nod ahead of first choice goalkeeper Petr Cech for the clash against the Greek champions. The Colombian international was at fault for Olympiacos' second goal during the 3-2 defeat at the Emirates Stadium. But Wenger was quick to defend the former Nice stopper, whose place has been usurped by the Czech Republic international as the club's number one, claiming that all players are prone to mistakes at some point in their careers.