#4 Declan Rice (West Ham United)

Declan Rice is a 20-year-old defensive midfielder who currently plays for West Ham United in the Premier League. He has featured for the Republic of Ireland's national team, but recently made the switch to play for England instead.
Rice has gone from being a bench-warmer to a solid first team player in the space of a single season. So far this campaign, he's featured in 28 matches, scoring two goals in the process.
This is exactly the sort of player City need as he'd be the ideal long-term replacement for Fernandinho and is also a home-grown player, which immediately makes him more valuable than any foreign shortlisted players.
It may be difficult to sign Rice, though, not because of any transfer fees, but because he's at the core of the current West Ham side. He probably also knows that although moving to a team like Manchester City might be tempting, the likelihood of him playing as many matches in the league as he is now is rather slim.