Old grip

This discussion occurred on the course.
Someone has a driver grip that is so worn that the shaft shows in spots. It looks like one of those grip training grips.
It has contours now that his hands fit in.
Does this constitute a damaged club or one that is modified/altered thru wear from it's original condition. Is it legal for competition?
Just curious. I had never seen anything like it in my life.
Amazing the gentleman is a very good single digit hdcp.

It was a slow round with lots of time on the tee box. Way to much time!