Mikel Arteta has suggested Arsenal's defeat to Manchester United was a result of his side showing a "lack of discipline". “We are very disappointed we haven't won the game, because it was there for the taking," the Gunners boss said."We haven't won it because we lacked some discipline... we weren't ruthless enough in front of goal."Man United won 3-1 at Old Trafford, taking the lead in the first half thanks to new signing Antony. Bukayo Saka pulled Arsenal level after the break, before a Marcus Rashford brace secured United's victory.