The 35-year-old former England defender ended his first spell at Arsenal with a Champions League final goal against Barcelona in 2006 but was playing for NottsCounty in League Two earlier this season.
He made one appearance for the Magpies before leaving and then re-signing for Arsenal in January.
FROM MORECAMBE TO BARCELONA IN JUST SIX MONTHS What am I doing here? Morecambe's James Bentley gives Sol Campbell - then at Notts County - some close attention
That's more like it: A few months down the line and Sol Campbell is back in the Champions League against Porto
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 tomorrow 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.'
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