The centre-half was substituted in the 26th minute after he came off worse in an accidental collision with Jeff Schlupp, but not after returning to the field of play following treatment.
Asked why he took Koscielny off, Wenger replied: “Because I had been told he had nothing serious and that he can come back after two minutes with two clips on his head. That was the medical opinion. After that he asked to come off.
“He continued to bleed a little bit and didn’t feel comfortable moving. He was not concussed, he was open on the top of his head. He didn’t feel comfortable to head the ball after that.
“In one week he should be alright.”
Wenger also confirmed that Mesut Ozil and Alex Oxlade-Chamberlain had picked up knocks in the second half.
“It doesn’t look too bad but I don’t know more,” he added. “We had Ozil with an ankle and Oxlade-Chamberlain with a calf.”
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