Arsene Wenger has admitted that a "tactical mistake" cost Arsenal the game in their 2-1 defeat to Manchester United on Sunday.
The Russian allowed Antonio Valencia to come inside off the wing to set up the goal which caused much frustration for the Arsenal fans. The home crowd voiced their disapproval when Wenger replaced the impressive Alex Oxlade-Chamberlain for Arshavin in the 74th minute.
The French boss defended his decision but admitted that it was costly in the end.
"When it was 1-1 it looked like we would win but in the end one tactical mistake lost us the game," he told Sky Sports News.
"I do not want to dwell too much on that now but one second of inattention can cost you.
"You have an 18-year-old kid making his first Premier League start and a player who's captain of his country and they are querying the substitution? Let's be serious."
The defeat leaves Arsenal in 5th place, five points behind Chelsea.