Rio Ferdinand labelled Pablo Mari's defending against Romelu Lukaku an 'embarrassment' and said the Arsenal centre back 'didn't know what to do' to stop the Belgian.
The Gunners were beaten 2-0 by Chelsea on Sunday, with Lukaku getting the better of the Spaniard for the opening goal.
Mari could not match Lukaku physically and the striker held off the 27-year-old before laying the ball off and sprinting into the box to get on the end of Reece James' cross.
Ferdinand was critical of Arsenal's defence as a whole but highlighted Mari's poor attempts to compete with the Chelsea forward.