#1 Marquinhos
This might be a very controversial addition. After all, he is the best defender at Paris-Saint Germain and replacing him will be a really tough task. However, once you realize that PSG actually need money to balance out their FFP, Marquinhos suddenly becomes gettable.
At least for a fee in the range of Virgil van Dijk, he was.
The Brazilian is an exceptional talent who has the ability to see things before they happen—almost wizard-like. He might not be the tallest of defenders, but his aerial presence is still very strong. In him, Liverpool could have gotten a younger player with a higher upward ceiling.
Right now, after the transfer fee of the Dutchman has been known to the world, signing the likes of Marquinhos for anything below £100 million seems like something next to impossible.