#4 Nia Jax

Nia Jax got a lot of heat last year after she concussed Becky Lynch with a legitimate punch, forcing her to pull out of Survivor Series against Ronda Rousey. However, in hindsight, that accident would end up having a ripple effect that led to Becky Lynch main eventing WrestleMania and walking out as the double champion.
What people didn't know was that for a good part of 2018 and 2019, Nia Jax was pushing through injuries herself, with her knees reportedly not being in the best condition. A little after WrestleMania, Nia Jax confirmed on Twitter that she would be getting ACL surgery for both of her knees.
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She posted an update about it on Twitter as well. ACL surgeries usually result in 6-9 months of action being missed, which makes it clear that Jax won't be returning until early 2019 at the least.
A top WWE star is missing in action