Casino players here in my place are not prohibited nor required to wear face masks but the standard protocol has always been observed at the entrance;
everyone will have to remove their face masks, caps, shades, and whatever headwear they're wearing for identification and recording purposes.
That's is a good control and they need to strictly implement that as if one player carrying the disease can enter the place, it could easily infected the others, of course if they are gambling, it's very uncomfortable wearing a face mask, I wouldn't do that if I am constantly going into casinos.