Every manager has at least one. They are often on the fringe. They might even have potential, but for now, they are your unmotivated employee.
You can't even remember why you hired them. You can't ignore them.
You need every human resource to be fully engaged.
I suggest three meetings over three weeks. In meeting one (week one), state your concern using "I" to describe the problem more than "you". And ask how you can help them get engaged and become self motivated.
Week two, ask how the past week has been and where they think they have made progress. Week three, point out where you believe their performance has improved. But, if by week three, there has been little growth then you have to explain that their job is in jeopardy and set a hard date for improvement.
Your most valuable inventory gets in a car and goes home every night... they must grow or go...and that's your responsibility!