The Rotorua match is billed as an unofficial 'fourth test' and, after two losses already on their 10-match tour already, the Lions will be keen to put on a performance to show they could threaten the world champions the following week.
Coach Gatland was always expected to name his strongest team for the Rotorua game and 11 of the players who impressed in the 12-3 win over the Canterbury Crusaders last Saturday, the best display so far by the tourists, will start.
The 53-year-old New Zealander, however, said he had still not settled on his test team.
"Even though it's a strong side we've got to make sure we're not fully showing our hand," Gatland told reporters.
"We're keeping some combinations back and we need to keep the All Blacks guessing a bit about what the final squad is going to be."
One key selection, particularly given the late withdrawal of Owen Farrell from the bench, was giving Johnny Sexton a final opportunity to press his test claims in the number 10 jersey.
Farrell had edged ahead of the Irishman as the first choice flyhalf but could now be in doubt for the first test on June 24 because of a thigh strain.
The injury means Gatland will not get another look at the Englishman's possible combination with Sexton.
Farrell moved to inside centre when Sexton came on as a replacement against the Crusaders and Gatland said he felt they had looked "pretty seamless" as dual playmakers.
Tour captain Sam Warburton's performance from the bench will also come under scrutiny after Ireland's Sean O'Brien was awarded the start at openside flanker.
Warburton arrived in New Zealand under an injury cloud having not played since April due to a knee problem, only returning to action in the opening match of the tour.
The Welsh flanker scored a try in Tuesday's loss to the Otago Highlanders and Gatland said he needed to perform off the bench to show he should start against the All Blacks.
"One of the reasons that we selected him as captain of the squad is that because he's an absolutely quality player, but also that this tour isn't Sam Warburton, it's about putting the squad first," Gatland said.
"So if he's not involved in the first test because of the performance on Saturday, he will fully understand that."
The Maori backline would not look out of place in a New Zealand test team and will be anchored by flyhalf Damian McKenzie, an electric runner of the ball who missed out on Steve Hansen's squad despite winning two caps last year.
The 22-year-old has been transformed into a fullback at the Waikato Chiefs but the All Blacks are keen on seeing him play more often in the pivotal flyhalf role.
"I haven't had a really good crack there so it's obviously a good opportunity this weekend and hopefully I can make the most of it," McKenzie told reporters in Rotorua.
(Reporting by Greg Stutchbury; Editing by Nick Mulvenney)
