Kevin-Prince Boateng’s early strike, two goals by Robinho and a penalty from Zlatan Ibrahimovic look to have put the last-16 tie beyond the Gunners, despite the return leg at The Emirates in three weeks’ time.
But Arteta, who joined Arsenal from Everton in August, insists the London outfit cannot afford to dwell on the result and they must instead turn their focus to a difficult trip to the Stadium of Light.
“We have to try to digest this result,” Arteta told Arsenal’s website. “We have another great game on Saturday in the FA Cup and there are some big ones coming up soon.
“We have to be mentally ready when we get back because it will be a very tough game against Sunderland. It is very, very hard to take this one.
“We need to be positive, take the bad things we have done tonight and improve them.
“We were expecting a different game but we found it very difficult to create chances on the floor like we wanted to and they were the better team. Every time they managed to get the ball out from the back on the floor and create a problem for us. We are very disappointed, it’s a big result to take.”
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news