Greater Manchester Police have said that a 30-year-old man has been released after being questioned, and that investigations into the alleged data breach are ongoing.
A police spokesperson said: "Greater Manchester Police are currently investigating allegations made regarding the Computer Misuse Act.
"A 30-year-old man was arrested on suspicion of offences under the Computer Misuse Act 1990.
"He has been released under investigation."
A report in The Sun newspaper claimed that an IT contractor has spoken to them about emails that apparently contain players’ contact details and private transfer discussions, with a number of players said to have been mentioned.
The newspaper also reported that Guardiola was the target of an alleged blackmail attempt after the Spaniard was targeted by a man who was attempting to sell the details for £100,000 in 2017.
A City spokeswoman said: "While we had terminated the services of this consultant and the company he was contracted to two years ago, we were unaware of the serious crimes he is alleged to have committed whilst working with us and the subsequent alleged attempts to profit from those crimes.
"It is a matter of public record that we have been the target of several criminal attacks through our IT systems in recent years."