The Gunners had an agreement to sign Toure in 2003 after he impressed on trial, but instead the Ivorian opted to join Metalurh Donetsk.
Arsenal needed to wait on a work permit for the 6ft 3in powerhouse, but the delay ended up with Toure heading to Ukraine.
“At the top,” Wenger joked when asked how high the 30-year-old ranked in his signing regrets.
“But let’s not forget Toure had an agreement with Arsenal. We waited for his passport in Belgium but he went to Ukraine [instead].
“He’s not a mistake but he preferred to go to Donetsk without a passport.”
Wenger’s Arsenal take on City and Toure tomorrow.