The court heard six hours of arguments on Monday before going into deliberations. After several hours, it announced it would issue the decision at 10 a.m. (0900 GMT) Tuesday, an unusual but not unprecedented move.
The high court normally issues the decisions the same day it hears arguments. But prosecutor general Luigio Riello told reporters that "in very complex cases, it happens" that the court takes another day.
Lawyers for Knox's co-defendant, Raffaele Sollecito, declined to speculate on what the delay could mean for the decision. Both were acquitted in 2011.