The Daily Mirror says the Premiership side are close to completing the signing of the 23-year-old.
Former Manchester United ace Jaap Stam played with Vermaelen at Ajax and believes the Belgian can become one of the best defender in Europe.
“I liked the way he was defending as a youngster,” Stam is quoted as saying.
“I think he was only 19 when he had made his debut. But he was a quick learner and strong in tackles.”