Ferdinand made the comment during the Gunners’ Premier League match against West Ham at the Boleyn Ground on Saturday afternoon.
Arsene Wenger’s side were 2-0 up at one stage, but they conceded twice in the closing stages of the first half.
England international striker Andy Carroll scored both of those goals and completed his hat-trick in the opening minutes of the second period.
Arsenal's defensive frailties show themselves again. If Wenger doesn't invest in a CB in the summer then I will be amazed....again!— Rio Ferdinand (@rioferdy5) April 9, 2016
Arsenal are a brilliant side to watch and are superb going forward, but defensively they remain vulnerable.
The way the North London outfit allowed West Ham to claw back a two-goal deficit and then go ahead suggests that Wenger needs to address the defensive issue in his team.