The All Blacks and Lions meet in the first of three tests at Eden Park later on Saturday.
Coles had been named in the All Blacks squad for the series despite battling a succession of injuries this season, including concussion that had kept him out of action since March.
"He (Coles) is clear of most of his symptoms and he is back training," Hansen said on allblacks.com. "But because he is not fit enough to play test rugby, or Super Rugby, we have put him back into what we call a pre-season training block.
"He will stay with us for the next three weeks then go back to his franchise and be back to play when he's rugby ready and fit enough for the rigours of Super Rugby."
The Wellington Hurricanes hooker was initially hurt when he limped off with a knee injury in his side's 41-15 win against the Otago Highlanders on March 18.
Coles was then kept out of the team with a calf injury sustained in training before Hurricanes coach Chris Boyd confirmed in early May that he was also suffering from headaches and other concussion symptoms.
With the headaches brought on by exercise, Coles has been unable to re-establish his fitness base, however, Hansen named him in the All Blacks side for the Lions series anyway.
Highlanders hooker Liam Coltman was named as one of five additional injury cover players for the All Blacks in case Coles did not recover in time.
Codie Taylor has assumed the mantle as the first choice hooker in Coles' absence, with Nathan Harris coming off the bench.
The first test between the All Blacks and Lions kicks off at 7.35 p.m. (0735 GMT).
(Reporting by Greg Stutchbury; Editing by Amlan Chakraborty)
