The form of Laurent Koscielny and Per Mertesacker saw the Gunners' captain lose his starting place last season and he will seek a fresh challenge after the World Cup.
The Gunners' captain wants to find a new club after slipping down the pecking order at Emirates Stadium over the last 15 months.
Arsenal expects the Belgian to become the second senior defender to leave in this window following Sagna, whose transfer to Manchester City on a three-year deal was confirmed on Friday.
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Vermaelen has only a year remaining on his contract and Arsenal is unlikely to stand in the way of a move if the club receives an offer that matches the club's 10 million euro valuation.
Manchester United and Napoli are among the clubs closely monitoring the versatile defender's situation.
The 28-year-old is expected to be a key figure for widely fancied Belgium in the World Cup, starting alongside Vincent Kompany in the center of defense.
A strong tournament could increase interest across Europe in Vermaelen and give him more options later in the summer.
The Belgium international has been the third-choice center back at Arsenal since an error-strewn display in a 2-1 derby defeat to Tottenham in March 2013 prompted Arsene Wenger to make Per Mertesacker and Laurent Koscielny his preferred central defense partnership.
Mertesacker and Koscielny have both signed contract extensions in recent months, keeping them at the Emirates until 2017 and 2018 respectively.
Arsenal will be in the market for a new center back if Vermaelen ends his five-year spell at the club.