Arsenal made the tough decision to sell Emiliano Martinez in the summer.
The Argentine took his chance at the end of last season when Bernd Leno was ruled out through injury.
Martinez deputised brilliantly as he produced some assured displays in goal.
He played a starring role as Arsenal won the FA Cup. He also helped them win the Community Shield this season.
But Leno resumed as Mikel Arteta's number one when he made his return from injury.
Martinez was subsequently relegated back to the bench.
The 28-year-old had had enough and he was transferred to Aston Villa for £20m.
This is a decision that has been slammed by Tony Adams.
Speaking on Sky Sports' The Football Show, Adams said: "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.
"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."
View his comments at 4:20 below:
GIVEMESPORT'S JAMES STROUD SAYS:
I think Martinez is a great goalkeeper. He was superb last season for Arsenal and he's been a major part of Aston Villa's great start this campaign.
But I don't share Adams' view that selling him was a mistake. At least for now.
Firstly, Leno is a great goalkeeper himself. He's been solid between the sticks for the Gunners ever since his transfer from Leverkusen.
He's much more experienced than Martinez and, unlike Martinez, has played at the top level for the majority of his career.
Secondly, Martinez wanted to go. I admire Arteta and Arsenal for letting a player leave that had been at the club for 10 years.
If Martinez continues to play at a high level and Leno's form dips, then it can be considered a mistake.
But Adams' comments are harsh with Leno still performing very well.