The Belgian defender has endured a miserable time at Barcelona since leaving London for the Nou Camp in 2014.
Vermaelen still has two years left on his contract with the La Liga giants.
Previously, in his career, the Belgian worldwide had a successful spell at Arsenal, it remains to be seen whether the player fancies a second spell in London playing in the EPL.
He came to Selhurst Park with a reputation of being one of the best goalkeepers in France, but his tenure in England will go down as a major disappointment.
Un Français, soupçonné de projeter un attentat présenté à un juge
Il est accusé d'avoir projeté un attentat avec deux frères arrêtés mercredi à Anderlecht, Akim Saouti et Khalid Saouti. Un arsenal composé de kalachnikovs et détonateurs, ainsi que d'uniformes de police, a été découvert en Belgique.
He remains keen on bringing Mamadou Sakho back to Palace permanently following a hugely successful loan spell last season.
Therefore, a move for Vermaelen would offer De Boer a much cheaper alternative.
The Dutchman has made just 21 appearances for Barcelona since the start of the 2014-15 season.
The experienced star has won 58 caps for his country and previously played for Ajax before joining Arsene Wenger's side in 2009.
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