The WWE announced on Monday afternoon that Shane McMahon has been hospitalized due acute diverticulitis and an umbilical hernia.
The article on the WWE’s website states that McMahon was on vacation in the Caribbean with his family and developed “a massive infection due to acute diverticulitis and was hospitalized for several days in Antigua before being flown back to a New York-area hospital”.
An umbilical hernia is going to require surgery once the infection is taken care of.
If the idea was to tease that Shane would miss WrestleMania, they would not make up an illness and instead credit the attack by Kevin Owens and Sami Zayn, so I feel most would assume this is legitimate.
Given that Shane will require surgery, it would seem nearly unlikely that he would be able to work WrestleMania in less than two-weeks.