Arsenal were just seven minutes away from claiming what would have been a superb come-from-behind victory at the Emirates Stadium on Saturday, as goals after the break from Jack Wilshere and Alexis Sanchez eclipsed Sergio Aguero's opener.
It was not to be, however, as Martin Demichelis crashed home an 83rd-minute header from Aleksandar Kolarov's cross after being left unmarked in the penalty area.
Wenger praised his side for coming back into the match, but was disappointed with the sloppy nature of the equaliser.
"It was a game of top quality between two very good teams, especially in the first half, we were unlucky to be 1-0 down," the Arsenal manager said.
"We did remarkably well to come back and be in a leading position. The only disappointing thing for me is we weren't able to keep hold of the lead and gave a cheap goal away.
"It's a very encouraging game but the way we conceded the goal almost killed our game because it was a mental blow and we could have lost after that."
There was a blow for Arsenal shortly before City's equaliser when full-back Debuchy caught his studs in the turf and had to be replaced.
Wenger confirmed the France international had suffered an ankle sprain, but is unsure how much action he could miss.
"Debuchy has a badly sprained ankle, for how long he will be out we do not know but it does not look too good," he added.
"People told me they need a bit more time to assess how long he will be out but it's a bad ankle sprain."
