He made one appearance for County before leaving and then re-signing for Arsenal in January.
But even Wenger admits he is surprised by the change in Campbell's fortunes as Arsenal prepare to face Barcelona in the first leg of their Champions League quarter-final at the Emirates on Wednesday night.
"It is unbelievable," said Wenger. "He played at Notts County six months ago. That he can turn up and play against Barcelona is quite amazing."
Barcelona 11/8, Arsenal 15/8, Draw 2/1