Tony Adams has criticised Mikel Arteta's decision to lose "one of the best goalkeepers in the country" by selling Emiliano Martinez in the summer window.
Martinez impressed for the Gunners last season after a season-ending injury to No. 1 Bernd Leno, playing a vital role in the club's FA Cup triumph.
But after it became clear Arteta would not give him the first-team minutes he wanted, Martinez sought a move away from the Emirates.
The Argentine shot-stopper joined Aston Villa for a fee rising to £20million and has impressed in his first seven league games for the club, keeping four clean sheets.
Meanwhile, Arsenal have kept just two clean sheets this season with Leno between the posts - and Adams insists Martinez should have stayed on as the Gunners' first choice.
The former Arsenal captain told Sky Sports: "I always said if Arsenal want to win the league again they need the best goalkeeper and for me, Leno is not the best goalkeeper.
Was it a mistake to let Emiliano Martinez leave Arsenal? Have your say here.
"I’ve called into question with Martinez being let go. That was a mistake for me. I think he’s come of age and he performed excellently last season.
"Why would you - a club wanting to win the league - let go one of the best goalkeepers in the country? I don’t see that as a good decision."
Martinez made a dream debut for Villa in September, saving a penalty and keeping a clean sheet in the 1-0 win over Sheffield United.
In light of his performances, the 28-year-old - who featured for his country at under-17 and under-20 level - has been called up for the senior Argentina team.
He may make his long-awaited debut in the World Cup qualifier at home to Paraguay on Friday or away at Peru next Wednesday.
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