The Gunners' boss believes the Belgian defender is finding it difficult to cope with the additional responsibility and pressure that comes with wearing the skipper's armband
The 26-year-old has been criticized for a number of mistakes in recent weeks which have contributed to Arsenal's unimpressive run of results.
Wenger revealed the Belgian often thinks about his performances all day after a match, but insists that despite his relatively poor recent displays, he is deserving of a starting place, captain or not.
"On Tuesday [away to Schalke in the Champions League] he was outstanding," Wenger told The Daily Mail. "I think what has happened to him in recent weeks has affected his confidence.
He added,"Physically he has no problem. You put more pressure on yourself when you are the captain. You want to be the best player in the team. You cannot be a defender and not make a mistake.
"But if you make one then maybe you put a bit more pressure on yourself, because you think, 'I’m captain and I cannot afford that'.
"He is a guy who is completely involved in the game. He breathes his football from morning until night. He thinks about it and wants to do well."
Vermaelen filled in at left back against Schalke, with Andre Santos dropping to the bench, and is expected to return to the heart of Arsenal's defense for their game against Fulham on Saturday.
"If he deserves to play, I play him. Captain or not, I think he deserves to play. He can help our stability at the back. That is important," he said.