He's the only TOTY I've ever packed, and I was originally a bit unsure of what to do as I'm using a BPL squad and he was untradeable. I also didn't want to waste such a good card at fullback so I did some rather convoluted positioning changes to get him as the RDM in my Premier league 4-2-2-2. Originally I used (CAM positioned)Fabinho at CB, moved (CDM)Rashford up to CAM, and put Marcelo at RDM, but I've since added Flashback David Luiz and changed it up a bit (you can follow the link to my current squad). He is far and away the best box to box CM I have ever played with. His passing and dribbling are great, but it's his physicality and reactions that allow him to totally dominate the midfield. Almost all of my play goes through him, and with Marksman he's enough of a longshot threat that he can't be defended against conservatively. Add in 5 star skills and he forces the opposing defense to be perfect.
I have him set to join the attack, which (with his 99 positioning) also makes him a threat to occasionally cut into the box, and an aerial threat on crosses when the CBs are busy marking strikers. Any time I'm on the wing, I either have Arnautovic, Lukaku or Marcelo mismatched against someone in the box. Since he's at CDM for me he pretty much always gets back into position, but I imagine at CM his low defensive workrate may be a bit of a problem. Although I'm sure he'd be fine as long as he's matched with a high WR partner, especially considering his pace and stamina allow him to catch up to most CMs pretty quickly. He's the centerpiece of my team, and is everywhere on the pitch. Well worth the 1 million if you're looking to control the midfield.
Very hard to muscle off the ball/ great shielding
Excellent dribbling and 5 star skills
Effective playmaker anywhere on the pitch (good vision, passing and crossing)
Dominates the Midfield
Longshooting and in the box threat
Excellent offensive support
Wins the ball back in the Midfield
Short for a LB for his price (excellent in the midfield though)
Low defensive WR
Ultimately, not really the anchor of a defense
His position requires some creative squad building to maximize value