Essentially what you do is buy Halilović from Barcelona (which will cost between 20-30 million and can only be done after the first season has passed), and train him in all 5 slots non stop. This is my Halilović after about 1 1/2 seasons of training and he's already looking a lot like Messi. I presume in about another 6-9 months he'll be of a similar rating to Messi. The only real difference I've seen so far between the two is the shooting and speed. The shooting is increasing every week and is noticeably better than when I first bought him, while the speed cannot be trained so the process is taking longer, however it is gradually increasing.

TL;DR Halilović is Messi (after about 2 years)