As we reported last night, Taker had hip surgery recently (apparently on his other hip) and it has been confirmed by Tim White. Along with that comes confirmation from Undertaker's wife, Michelle McCool.
The picture you see of the Undertaker on crutches going around is because he had hip surgery confirmed by his wife on Facebook.— Tim White (@RefTimWhite) October 16, 2016
It's no surprise The Undertaker has had issues with his hips and body over the years.
The Tim White Twitter account shared on this post seems legit. Jim Ross, Mauro Ranallo, Bob Evans (no not the restaurant), and a few other verified people who have affiliations in the pro wresting world followed him. You can see here