I was demoted from my supervisor job when I went in to tell them I was going to have to have my 3rd hernia surgery. My boss wanted to do it right then but human resource said they would pay me supervisor pay until I come back then I have to go back to flo

Prudential our short and long term disability. My company was being bought out while I was out. My human resource called on a Tuesday and said they had to have all the doctors notes from my doctors before Friday. This was January 2016. I had been on medical leave since late August 2015 and was told I was demoted when I come in and told them I was going to have to have another hernia surgery. This would be my Third one since 2014 and I also had a left knee operation because of a torn meniscus in 2015. My supervisor come in and said he had to have a supervisor on that shift and immediately wanted to move me back to floor work on night shift and the human resource lady and my supervisor decided it was to dangerous for me to be on the floor at that time and wanted me to take my fmla then( August) instead of waiting till September when my surgery was scheduled. The human resource lady said they would pay me my supervisor pay while on my short term and when I come back they would move me to 3rd shift and put me as a tube mill operator. After the surgery my doctor told me I would not be able to lift anything over 20-25lbs. Floor work required me to be able to lift up to 50lbs. Prudential said since I started the claim as a supervisor the restrictions I had ment that I could go back as a supervisor. Which was not a option. I did come back and tried to perform the floor job but unable to do it and am now filing for Social Security disability but because I'm only 45 the disability may not go in my favor is what my SSD lawyer told me. I just want to know if my demotion was legal because I had gotten a good review on my employee evaluation?