The former Portsmouth stopper, who joined Arsenal on a free transfer from bitter rivals Tottenham Hotspur in 2001, won three FA Cups and two league titles during his five-year spell at Highbury.
Despite reported interest from Everton and Aston Villa, the 34-year-old has opted to sign a five-year deal with the ambitious basement division outfit, who - backed by the millions of Munto Finance - have appointed ex-England coach Sven Goran Eriksson as director of football and signed Manchester City goalkeeper Kasper Schmeichel for a club record fee.
But Wenger believes the move is a big step down for someone who has never played outside the top flight of English football.
"It was a surprise, because of the level Notts County play at. That shows you as well how much financial potential Notts County has suddenly," he said.
"Time will show if it is a good move for him. It depends what is in his mind, if it is purely a football move or if it is a long-term move that he wants to be involved afterwards as a coach.
"Maybe it can be a good decision if he wants to build something on the longer term. On the short term, he will suffer a bit because he is used to top-level football.
"When you move down, it is always difficulty to cope mentally."
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