During a match that pitted Ciampa and DIY partner Johnny Gargano against Sheamus and Cesaro, the current NXT Champion attempted a sunset flip powerbomb on the larger Sheamus. When Ciampa's feet hit the canvas after the initial rollover, his feet either skidded or one of his knees buckled, which caused Ciampa to crumple to the mat in an awkward sitdown, and for Sheamus to come crashing down on Ciampa's left leg.
Immediately, Ciampa grabbed his knee in obvious pain, while Sheamus rolled around painfully as well, clearly favoring his back. The referee made the "X" gesture to signify an injury.
According to Sean Ross Sapp of Fightful, both men were saying they were "fine" backstage, although that could simply be a preliminary declaration. Sapp did qualify his update by noting that Ciampa worked through a very serious knee injury for several days two years ago, and eventually missed nine months as a result.
Hopefully, both Ciampa and Sheamus (who himself has had issues with spinal stenosis) both officially turn out to be okay, and that the accident was little more than just a scare.