The Belgian has been ruled out for two to three weeks after limping off after 54 minutes at Emirates Stadium as the Gunners moved up to fourth with a 1-0 win over QPR, adding to Wenger's defensive injury woes.
Vermaelen, normally a centre-half, had been playing at left back following injuries to Andre Santos and Kieran Gibbs. And with Bacary Sagna and Carl Jenkinson also on the long-term injury list, Wenger admits he will look to bring in defensive cover on loan.
"We lost Vermaelen for two or three weeks, so I have to look if I can find somebody [but] only a loan," he said. "It would be stupid for us to drop points because we don't have a left-back.
"[Vermaelen's injury] is serious enough for him not to play on Monday against Fulham or against Leeds. We now have three left-backs out. Francis Coquelin came on in this position and did quite well, but he is a central midfielder."
Wenger is set to boost his attacking options with the return of former Arsenal captain Thierry Henry on a two-month loan deal. And Wenger, who first brought in Henry from Juventus in 1999, is confident the Frenchman can strike up a successful partnership with top goalscorer Robin van Persie.
"I don't think he [Henry] will get international clearance for Monday but he has a little chance to be available for the Leeds game," Wenger said. "They can play together, it can hopefully give little breather to Robin as well. Thierry is there to help out. He can also help in the dressing room.
"He will bring us his class. In training, he has still exceptional class and he might surprise a few people."