If true.... gotta wonder about the source of this rumor.
Let's suppose it is true, though. The introduction of a 3rd candidate into the debates could (depending on the candidate) be catastrophic for both Trump and Clinton.
The bar for such a person would be pretty low: to earn votes, he'd only have to present himself as sober, responsible, and reasonably honest; and have a reasonably good grasp on the issues.
Now.... would I vote for Gary Johnson in preference to Trump or Clinton? Hell, yes.
Not too happily, mind you -- the guy's got plenty of problems of his own. But he's better than either of the others; and if he has a legitimate shot at affecting the election results then I'm for him.