Former Arsenal defender Martin Keown says the rearguard made things too easy for Erling Haaland during Wednesday's 4-1 thrashing at Manchester City.
Keown was baffled by the lack of aggression shown by Arsenal's defenders on the night.
"If I was playing, Haaland would be all I was thinking about," Keown told BT Sport.
"(Rob) Holding lost that battle. The very first challenge, that's where they concede the first goal.
"You've got to put your marker down, you've got to be physical, maybe take a booking.
"But Haaland is just strutting around that pitch and it looked really easy at times.
"That's something these young Arsenal defenders are going to have to learn, and learn quickly."