Koscielny started the 2011–12 season alongside Thomas Vermaelen in central defence. Koscielny was injured and taken off the pitch 10 minutes into a 2–0 home loss to Liverpool on 20 August 2011. However, he returned to the starting line-up Arsenal's biggest ever Premier League defeat, losing 8–2 to Manchester United at Old Trafford. On 17 September, Koscielny scored an own goal as Arsenal lost 4–3 to Blackburn Rovers in the Premier League. He went on to be named man of the match away at Olympique Marseille in the Champions League, where Arsenal won 1–0 at the Stade Vélodrome, keeping their first clean sheet in a Champions League away game since 18 August 2009 against Celtic, where the Gunners had won 2–0.