10%, probably less but maybe closer to that than <1.
The real reason we've been hearing some mixed signals about the injury probably has to do with this (from ESPN preview):
"The Magic wrapped up their series against Philadelphia in six games on Thursday, and apparently have time to spare: They watched film of Garnett on Sunday, skeptical of whether the injured star is really out for the playoffs as the Celtics maintain."
Even if KG can't come back at all, we want it in the back of our opponents' heads that he could. The more time they devote to planning for him, and the more uncertainty they have about a comeback, the better off we are.