The 28-year-old Belgian has been linked with a move to Manchester United.
"At the moment Thomas Vermaelen is here. He is injured at the moment with a short-term injury. It could happen, yes it's a possibility that he goes. If he goes we have to replace him because he's an important player in our squad," Wenger told a news conference.
"I expect him to stay but he, of course, did not play enough games last year. For me he's a very important player but I couldn't guarantee him the games he wanted last year."
Wenger has recruited Chile forward Alexis Sanchez, France defender Mathieu Debuchy, Colombia goalkeeper David Ospina and young English defender Calum Chambers.
He denied reports that he was trying to sign Porto playmaker Juan Fernando Quintero but said further moves in the transfer market were possible.
"I am very happy because I did what I wanted and I am still hoping to do more," he said.
"We are a bit ahead of what we usually do because the availability on the market was bigger than before. I think 15-30 August will be busy again."
Wenger played down comments by Liverpool captain Steven Gerrard that Uruguay striker Luis Suarez was too good to move to Arsenal who were interested in signing him 12 months ago.
"You're never too good for Arsenal and Steven Gerrard knows that," Wenger said.
"But I can understand completely that he asked him to stay because he wanted him, to play with him and have a chance to win the Premier League. But it didn't happen, and anyway, Suarez left," Wenger added, referring to the Uruguayan's recent move to Barcelona.