The Frenchman has previously come in for criticism for his dealings in the transfer window due to a perceived reluctance to spend big.
However, Wenger believes he should be praised for Monreal's arrival, a move which was only prompted by an injury to Kieran Gibbs the day before the transfer window's close.
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"And we found in 48 hours a player of that calibre... you have to give me at least that credit. I know that I don't get a lot but that is true."
The 63-year-old went on to hail his side's doggedness as they posted a 1-0 win over an obstinate Stoke at the Emirates Stadium on Saturday.
"We are a bit more mature now, but we dealt well with [Stoke’s game plan]," Wenger added. "[Peter] Crouch is a handful because he is not only physical, he is technically very good. He uses space well and in his link-play he is an international player. Overall I think we had a serious game.
"We were a bit younger and inexperienced [in the past] but defensively today you could see that in [Bacary] Sagna, Nacho, [Laurent] Koscielny and [Per] Mertesacker we have some experience and stature there. We are not small at the back.
"In England you have to deal with all types of football without losing your qualities in how you want to play. It is not always easy, because if you have a team of 10 Santi Cazorlas technically you would be very good but against a team like Stoke you would struggle."
Wenger was also full of praise for Theo Walcott, who has continued his fine run of form since signing a new contract at the club.
"He is 23 years old and there is always a change at that age," he continued. "What people forget is that Theo does everything at 100mph, so every time you get hit it hurts you more than if you are slow.
"He plays at high pace, but he has learnt to escape sometimes and he imposes himself more. He uses his body better now."