Gibbs limped off in the first-half of the clash with Partizan Belgrade on Wednesday.
Wenger said: “Keiran Gibbs has a twisted ankle, an ankle sprain. I don’t know how damaged his ankle is – he will have a scan tomorrow. He is unbelievably unlucky.
“No [it is not the same ankle he injured recently], it is the right one tonight. I spoke to him, he is quite down. He is on crutches. I cannot tell you more. We will know tomorrow but he is already out for Monday night.”