Police arrest semi-final ticket thief
Two special delivery bags containing the tickets were stolen from a Royal Mail van close to City's ground in Manchester on Friday.
Greater Manchester Police said they had arrested a 39-year-old man on suspicion of theft on Tuesday after a number of addresses were raided.
He has been bailed pending further inquiries. Media reports identified him as a post office worker.
Police said they feared the tickets for the derby clash between the fierce rivals on April 16 were to be sold on the black market. No tickets have so far been recovered by police.
In a statement on their website, Manchester City said: "All supporters impacted by the theft will be contacted by the club in the coming days.
"Only tickets purchased direct from the club will be valid for the game."