The overall success of a soccer player is not a good indicator of his potential as a coach.
There's a certain level of experience that is expected of a person interested in managing a football club, and that's why, more often than not, managers are former players who know the ins and outs of the grueling season.
While you never know what's going to happen unless you are given a chance, and there are great managers who were mediocre players and vice-versa, the common theme is that managers often played football before they started coaching.
We'll have to suspend a bit of disbelief when talking about coaches who can still play, the beauty of soccer though, or any sport for that matter, is that natural ability doesn't necessarily go away.
There may be some wear and tear on the body, but skills can endure.