#5 Robert Lewandowski
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He's been linked with Real Madrid for a long time now, even before Ronaldo's departure, and even before his move to Bayern Munich. There's no doubt he's a world class player, and one of the top strikers in the world.
However, he's already 29 and will turn 30 before the end of the transfer market. While he's definitely not yet past his prime, he's getting up there, and it would not make any sense for Real Madrid to spend upwards of €100 million on a 30 year old player.
However, we are on the topic of possible replacements for Ronaldo, and he definitely is one. He has been an incredibly consistent goalscorer in the Bundesliga, having been the league's top scorer thrice already. He has an incredible eye for goal, and would be a welcome addition to any team.