"This is hard for me to say, Korra, but..." His frown deepens, and he places a hand on her shoulder, as if to brace her. "It weakened you so entirely that you were left unable to walk. After we'd last parted ways, you were to travel to the Southern Water Tribe for treatment."

He doesn't say it outright, but the implication is there that she wasn't expected to recover quickly. Was her sudden jump back in time the Spirit World's way of getting the Avatar back on her feet? Or was it unintentional, entirely a random occurrence? It's impossible to guess.