#4 Harry Kane

The British goal machine has had a fantastic few seasons for Tottenham Hotspur since he came on the scene during the 2014-15 season. Since then, he's scored a minimum of 20 goals per season in the Premier League, even reaching a high of 30 Premier League goals last season.
Although he's not a like for like replacement for Ronaldo - playing as a central striker while Ronaldo played on the left wing, he could definitely fit into the Real Madrid front line, maybe forming a strike partnership with Karim Benzema, or more likely being a more dynamic replacement.
Either way, he is a proven goalscorer and could definitely help fill the void caused by Ronaldo's departure. Of course, he signed a new contract at Tottenham this summer, and that probably means he won't be wearing the famous white jersey anytime soon, but he represents an interesting option to say the least.