According to The Wrestling Observer Newsletter:

Aside from his back and knee problems, The Big Show also has an abdominal hernia that needs surgery.

It’s not a done deal regarding Wrestlemania 23 yet, but the feeling is that he will be doing the show. Big Show’s contract expires in February and he will be a free agent when the event comes around. Hulk Hogan and Big Show are friends and may do something of a big package deal together for Vince if he wants the rumored match between the pair

Despite the rumors, right now TNA Wrestling is under the impression that Big Show will likely never be working with them.