According to multiple sources, The Undertaker's status at WrestleMania 29 is up in the air due to health concerns. No specific details, but his physical condition is being said to be enough of a concern to put original plans on hold.
It's been heavily rumored that Taker would be facing CM Punk at WrestleMania this year. If this falls through, it would leave CM Punk without a match on the card and may force WWE to rethink all plans.
Any updates we hear, we will certainly pass along.
Sources: PWTorch, Wrestling Observer, and PWInsider.com