#4. Big Show - Could miss WrestleMania for the fourth year in a row
Big Show hasn't had a WrestleMania appearance since 2017. Even then, he was eliminated from the Andre the Giant Memorial Battle Royal, and he has only appeared sporadically in the last few years.
An appearance at WrestleMania 37 is unlikely unless WWE is planning to go ahead with the Andre the Giant Memorial Battle Royal. Even though the showpiece event is taking place at the Raymond James Stadium, it wouldn't be surprising to see WWE scrap the match due to COVID-19 protocols.
#3. Mark Henry
Just like Big Show, Mark Henry's last WrestleMania appearance was in 2017. However, it was post-WrestleMania 33 where Mark Henry fully transitioned into a backstage role.
He has been retired ever since, although one-off special appearances aren't out of the realm of possibility. However, that may only happen when crowds return. As of now, Mark Henry will likely be delaying any possible one-off appearances for WrestleMania 37.