The centre-back has struggled with Achilles and calf problems this season and will miss Saturday's Premier League clash with Newcastle United.
While Arsenal have splashed out on attacking talent such as Mesut Ozil, Danny Welbeck and Alexis Sanchez in recent transfer windows, questions have still been asked over whether the London club need to strengthen defensively.
However, Wenger insists if he has a fully-fit squad to choose from in January then he will not need to bring in reinforcements.
"If everybody is fit and available we don't need to go in the transfer market," he told Friday's pre-match news conference.
"We have to consider that Koscielny could be a question mark with his fitness and we have to go in the transfer market, yes."
Wenger also suggested January's window will be a low-key one, despite the likes of Manchester United and Liverpool both reportedly keen to bolster their squad.
"There will be very little activity because all the big clubs want to keep their players," he added.
"It will be as usual, quiet in the first three weeks and a bit more frenetic in the final three or four days.
"Usually the transfer market in January is not very active."
