Alan Shearer claims Arsenal's defence is "so bad it's unbelievable" and that the club could take up to three years to get back on track.
The Gunners were torn apart 3-0 by Manchester City in the Premier League on Sunday as the club remained ninth and seven points shy of the top four.
Arsenal's defence has been a key issue this season with their last clean sheet now dating back to October - a run of 14 straight games in all competitions.
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Shearer stressing that such shortcomings at the back should have been addressed in pre-season with the Gunners instead investing heavily in French attacker Nicolas Pepe.
"Arsenal’s biggest problem is recruitment, defensively they are so bad it’s unbelievable," Shearer wrote in his column for The Sun.
"Going forward they are fine because they have Pierre-Emerick Aubameyang and Alexandre Lacazette. But in terms of the quality of their defenders and midfielders they are miles behind the top teams.
"They spent £72 million on a winger in Lille’s Nicolas Pepe, when they knew they had big problems at the back. That made no sense at all.
"True, they were left high and dry when Laurent Koscielny suddenly wanted to leave so late in the transfer window but Arsenal’s defensive problems had been apparent long before that."
Still searching for a new permanent manager, Arsenal face a fight to secure a top-four finish this season and could miss Champions League football for a fourth straight season as a result.
After another poor showing against City, Shearer believes the club requires plenty of work to reach their former heights.
"The ease with which Manchester City beat Arsenal shows that the Gunners are miles away from where they used to be — and where they want to be," Shearer continued.
"It’s going to take a lot of time and a lot of investment to get them competing at the highest level.
"I would say at least two or three years and definitely a huge amount of money."
Arsenal next face Everton in the league on Saturday with the Toffees most recently holding Manchester United to a 1-1 draw.