The Gunners coach revealed the Sweden midfielder, signed on loan from Spartak Moscow, could be out of action until the middle of March.
The experienced Swedish international, who arrived on loan from Spartak Moscow on deadline day, aggravated the existing injury within half an hour of his first training session with his new club.
Wenger revealed that the former Lyon midfielder, who was signed as cover for the injured Aaron Ramsey and suspended Mathieu Flamini, will now be out until mid-March, but the cost of the Swede’s wages will be shared with his parent club.
"He arrived here and fell on his back two days before," Wenger said. "First of all, it's very difficult to identify a player who can come in of that stature on a free loan. We made a medical of his back and found out he had a little microfracture. We have all played with microfractures.
"Spartak Moscow accepted to share the costs. As long as he's injured, they pay. I had a decision to make. I take nobody or Kallstrom, on Friday after 5 o'clock."