Ouch!

I think you have to close off the skimmer--and fill the pipe with anti freeze. Or you can plug the low return, and then disconnect the pipe so the water drains out of it, and cover the skimmer so it can't get water into if. If you can't seal off the skimmer from the pool, then fill the skimmer with lots of foam--you can cut up a noodle and put the pieces in vertically--to keep ice expansion from splitting the skimmer. Standing water will expand when frozen and split your pipes.

That's my best guess.