Mix-and-match for All Blacks
New Zealand meet Namibia in a World Cup Pool C clash on Thursday.
All Black coach Steve Hansen said he would give minnows Namibia "total respect".
But for reigning world champions New Zealand the game at the Olympic Stadium is about looking forward with much harder challenges ahead.
Barrett and Slade are in the squad as cover for star flyhalf Dan Carter and for their utility value.
Slade will start at fullback against Namibia, while first-choice No.15 Ben Smith is on the bench, and Barrett will be at flyhalf.
But Hansen said they may swap roles for the second half.
"We'll see how it goes but you'll probably see both of them get a bit of a game" at flyhalf, Hansen said, adding Barrett would do the kicking in the first half and Slade probably take over in the second.
With Namibia unlikely to test New Zealand, the match has given Hansen the opportunity to field the balance of his squad who were not involved in the opening Pool C win over Argentina.
His first-choice selections came from behind to win the Wembley match 26-16 last Sunday.
Hansen explained it was now for the rest of the squad to get a taste of World Cup and push for inclusion in the starting line up in the knockout stages.
"Each team has to prepare in its own way. One of the things we pride ourselves on is trying to improve our performance from the previous one," he said.
"We put a line in the sand as far as the World Cup goes against Argentina and the group going out on Thursday have to change that line to a higher performance level.
"We'll give Namibia total respect because that's what they deserve as another playing nation. But rugby's a funny thing, if you don't prepare properly you can get a hiding."
In the build-up to the World Cup, neither Barrett nor Slade was given much opportunity to run the backline with the focus on working Carter back into form.
Their Test appearances so far this year have mainly been off the bench at full-back, with Slade also having one run on the wing and the pair, who both rate fly-half as their preferred position, have had little chance in the pivotal No 10 role.
"It's not ideal but you roll with it," Slade said. "We get enough opportunity there at training. We prepare well enough every week, regardless if we're playing, so if I get that opportunity I'm ready to go."
Agence France-Presse
