Platt admitted to City's website: "Obviously Roberto was a major factor in me coming here - I've known him for 16 years and he was instrumental in taking me to Sampdoria.
"When the phone call came it wasn't a difficult decision - I'm joining a club with great resources, a good strategy and good project to really challenge for things, coupled with a manager who I've got a great deal of respect for."
As well as renewing his partnership with Blues boss Mancini, he looks forward to working with assistant manager Brian Kidd.
He said: "Kiddo was working with Sven for England when I was with the England Under-21s. I've known him a long time and I'm looking forward to working alongside him from Monday.
"Brian's got the knowledge and involvement with the English game. What Roberto is trying to do is put together a staff that covers all aspects of the game here.
"For me it's a different role now - as a manager, the buck stopped with me. I have an opinion and I'm quite happy to voice it, but Roberto makes the decisions here.
"We had one or two rows when we played ... hopefully we won't be having them this time!"