The 29-year-old injured his knee for the Crusaders in early March and required an operation, only returning to the field in late May.
He went on to play all three British and Irish Lions Tests, as well as a protagonist's role in the Crusaders' Super Rugby triumph, but was rested from the All Blacks' two Bledisloe Cup Tests against Australia.
Characterising his knee niggle as a case of "old man syndrome" last week, Dagg went on to play just fewer than 50 minutes in Saturday's 39-22 win over Argentina.
But the issue appears more serious than Dagg intimated.