Were these suggestions from physicians?
If it was due to thyroid or statin, I think the problem will be more systemic rather than just affecting your hip / glute muscle. Have you had any labs drawn for your thyroid hormone and liver function (LFT)?
Tennis isn't the greatest sports for the hip. You might need to incorporate other hip and core exercises. I personally find core exercises much more helpful in alleviate my own hip problems. Chiropractor worked great for me, if you want to consider it.