The pair played together with the Gunners, where Arshavin was between 2009 and 2013.
Gallas told Ball Shorts: "It was too much for him. It was too difficult for him to be stable and maintain discipline.
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"I don't think he was strong enough mentally. Arshavin was indeed talented, but he did not have a great career.
"The Premier League is a very difficult league. It's not even about the fact that there are a lot of games there. You need to give yourself in training every day."