The All Blacks, who name their 31-man World Cup squad next week play Tonga in Hamilton on September 7th before facing South Africa in their opening Pool B clash two weeks later.
Hansen said he was wary of his first-choice players losing sharpness between last weekend's 36-0 victory over Australia at Eden Park and their World Cup opener.
"We'd like probably most of the frontliners to get some form of game-time in the Tonga game, otherwise it's too big a break before we play South Africa," Hansen said in comments published by Stuff Media.
Several of the players in the 34-man squad for the Bledisloe Cup tests have been released to play in New Zealand's provincial championship this weekend in order to give Hansen one final look at them before the squad for Japan is finalised.
One player likely to be under scrutiny is winger Rieko Ioane, who was dropped for Saturday's match against the Wallabies after being a virtual first choice since 2017.
Ioane will play for Auckland against Bay of Plenty on Saturday and while he is unlikely to miss out on the World Cup squad his starting place is under pressure.
Hansen gave rookie wingers George Bridge and Sevu Reece an opportunity against the Wallabies and both took their chance.
"We saw lots of energy and we saw lots of intent," Hansen said of the duo.
"They were great under the high ball, great chasing kicks so it's a bit of pressure on the other guys now to front up. There's the old saying 'never give a sucker an even break because he'll take it'.
"Now we've got some genuine competition."
Hansen added that tighthead prop, the midfield and the loose forward mix were areas that would create the most debate, with blindside flanker Liam Squire still in the frame if he made himself available.
Squire missed most of the Super Rugby season through injury and withdrew from contention for the All Blacks due to a lack of match fitness. Squire would be considered but he first had to tell the coach he was ready to return to international rugby, Hansen added.
The All Blacks have met Tonga five times previously, four of which have been at the World Cup. The only non-World Cup test ended in a 102-0 victory for the All Blacks in Albany in 2000.