I am in the process of removing an existing shower tray. I am having difficulty in removing the drain. It does not appear to screw in. I have access to from below if I need to cut pvc pipe. This appears to be the only thing keeping my tray in place at this time.

It sounds like you have a manufactured base and enclosure? If the drain's glued in you will have to cut the raiser to pull the base out. Good luck, Tom