Koscielny made his debut in European competition on 15 September 2010, when he partnered Sébastien Squillaci in a 6–0 win over Braga at the Emirates Stadium. Koscielny was praised for performances against Sunderland and made a brilliant tackle against Tottenham Hotspur to stop Aaron Lennon from scoring during their Football League Cup tie. On 27 October, he blocked a shot off the line and provided an assist to Theo Walcott against Newcastle United in the fourth round of the League Cup, where Arsenal went on to win the match 4–0 at St James' Park. Koscielny was given a straight red card in Arsenal's 0–1 loss at home against Newcastle United on 7 November 2010. This was his second sending off of the season.