It was not mandatory to be vaccinated to compete at the Olympics. It may have been compulsory for Australian athletes and officials, but we certainly went above and beyond the rest of the world with our covid safe measures.Thiem has struggled since winning the US Open, he did play a lot of tennis prior to winning his first GS. He needs a break.
I am actually surprised Stefanos wasnt even vaccinated for the Olympics, I also thought that was mandatory.
If it has not been compulsory for Tsitsipas to be vaccinated and he can still travel and play, then it is his call. I'm sure there are other players out there who are not vaccinated either.