The official word from the leafs says the same limited amount:

The first question most of us have is how long, exactly, has Jack Campbell been playing injured. The second question I personally have is why are the Leafs doing that again?

There is a possibility this is brand new, of course, but no one seemed to see anything hinky in the last game.

Two weeks takes the Leafs past this weekend’s outdoor game, past the trade deadline, and into the last 20 games of the season. It does not last long enough for Campbell to be on LTIR. Of course, if his recovery drags on, he can always be retroactively placed on LTIR to the date of the injury.

Update:

Turns out both theories of new/old injury are true.