Crusader Richie Mo'unga has joined the camp, although it was hard to gauge whether All Blacks coach Steve Hansen considered the young Crusader ready for action, should Barrett be ruled out.
Barrett left the field during the test in Cape Town nine days ago and did not return, despite passing the official head injury assessment.
Hansen said the star first five-eighths was training, but all was not well yet.
"He's been getting the odd headache - he's trained but afterwards he's not feeling hundy so we'll see how he goes during the week and if he's not right he won't play," Hansen said.
"He'll have to pass the tests we do as a team - it's about making good decision for the player."
With Lima Sopoaga and Damian McKenzie in the squad, Mo'unga is an unlikely selection. Hansen wouldn't rule him out but he said it would be a "big challenge" to get him up to speed so quickly.
"He's young, still in the infancy of his career and led the Crusaders well during the Super competition," he said.
"He's got a kicking game when he needs to kick, he can run, his passing game is okay. He's got the fundamentals of a good five-eighth.
"This is a different environment which comes with a lot of pressure, which can be overwhelming for some people. We'll do what we do with all the young fellas and take our time."