During a match with Bray Wyatt at last night's (Sat., June 7, 2014) WWE house show in Madison, Wisconsin, John Cena suffered an injury to his eye. While there are a few reports making the rounds from fans in attendance, one from the Wrestling Observer seems to be the most detailed.
About two minutes into the match, Wyatt had Cena backed into a corner and was hitting him with repeated headbutts. One of two things happened. Either one of the headbutts hit Cena in the eye, or some of Wyatt's greasy, stringy hair whipped Cena in the eye.
There's a much more detailed description of the events at the link here.
The referee did, in fact, throw up the "X" sign and Cena was attended to by medical personal. Because he's an insane person who works harder than any wrestler in history, Cena finished the match despite his eye apparently swelling shut.
WWE has yet to officially comment on the matter and Cena hasn't mentioned anything himself on his Twitter.
We'll see if he's showing any effects of the injury on tomorrow night's episode of Raw in Minneapolis, Minnesota. Stay tuned!