Sting's episode on WWE Untold was aired on WWE Network recently, and it showed Sting's last match against Seth Rollins at the 2015 Night of Champions PPV. 

He suffered a neck injury at the PPV after he took a powerbomb in the corner. It was later revealed that he had spinal stenosis before the match, and that suffering a stinger in the match was what showed that he had that injury, not because of the spot.  

Even though Sting's in-ring career is done, he is holding out hope that he can still have a confrontation with The Undertaker. 

“You know if everything lines up just right. Vince, Triple H, ‘Taker, and Sting, maybe we could do this. Maybe we could just do a little, let’s just do a face-off. Let’s get you guys involved in this or that. So maybe I could do it. Maybe I could do that. I don’t know, again, if it’s just ego and pride or whatever, but I feel like I could do it all these years later. It’s insanity, I guess I’m a pro wrestler for life”

Sting's done many interviews in the past which revealed he had always wished to have a match with The Undertaker.