According to a report in the DailyMail, United chief David Gill travelled to Croatia in a bid to sign Dinamo Zagreb's £15 million-rated young midfielder Alen Halilovic.
The 16-year-old sensation is tipped to surpass the likes of Luka Modric, attracting top European clubs including Real Madrid and the Manchester giants.
United are also keen on another City target defender Sime Vrsaljko. The 20-year-old right-back could follow Halilovic with a surprise £20 million double deal.
Mancini was left furious over the way City handled business during the summer transfer market. City lost out to United for the signature of Arsenal striker Robin van Persie.