Vermaelen was slammed for making a mistake which led to Robin van Persieâ€™s opener at Manchester United.
Wenger admitted: â€śThe error of Vermaelen was unwelcome. The big defenders donâ€™t make those errors.â€ť
Ironically, Vermaelen has taken over the Arsenal captaincy from Van Persie and Wenger believes the new role has been a factor in the playerâ€™s poor form.
The manager added: â€śYou put more pressure on yourself when you are the captain.
â€śYou want to be the best player in the team. But you cannot be a defender and not make a mistake.
â€śHe 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.
â€śPhysically he is outstanding. I think what has happened to him in recent weeks has affected his confidence. Overall, physically, he has no problem.â€ť