The Brussels club are on the lookout for a new centre-back to replace Bram Nuytinck, who signed for Udinese last week.
Reports in Belgium claim the Red Devil, who has 58 caps for his country, is on their wishlist.
Palace have been linked with a move for the 31-year-old defender, who was at Ajax during the time Eagles boss Frank de Boer was coach of the youth team.
Vermaelen spent last season on loan at Roma, who had an option to purchase, but the Italians decided they didn't want him after just a handful of appearances.
The injury-plagued defender still has two years left on his contract at the Nou Camp, where he earns £55,000 per week.