FIFA 18 Pro Clubs is in its early days so we can’t tell the exact max possible overall ratings that you can get with your online pro player, but based on skill tree and the player progression and on FIFA 17 max ratings here’s a prediction.
ST – 93
CAM – 94
CDM – 95
CB – 95
LB/RB – 95
GK – 93
On FIFA 17 there was a CAM with the highest seen 96 overall rating, but it was in very late FIFA 17 days, so the max rating may change over time, as you can progress more and more, but slower with time. Maybe in FIFA 18 there will be a certain cap, but this is unknown yet.
This post will be updated as more info about max players overall follows. If you see someone with a higher rating than listed above – let us know in the comments.