Tuesday's match in Hamilton is the last before the first test against the All Blacks and many pundits believe most of the side who destroyed the Maori All Blacks 32-10 at the weekend will run out at Eden Park on Saturday.
No players who started the Maori game will face the Chiefs.
Gatland, however, said that there were still test discussions to be had, with the versatile Liam Williams given the opportunity at fullback to push for inclusion in the test squad, while tour captain Sam Warburton is under pressure from Sean O'Brien for the openside flanker role.
"We won't sit down and pick the (test) team until Wednesday and I think that's only fair on the players that are taking the field on Tuesday," Gatland said.
"There's no doubt there's some pressure on him (Warburton) because certain players and certain combinations have gone well.
"The will be some discussions and debates to be had about the final make-up of the back-row for Saturday."
The machinations of the first test aside, the match holds strong feelings for Gatland, who played a then record 140 times for provincial side Waikato and scored a try in their 38-10 victory over the Lions on the 1993 tour.
Last year he returned with Wales to play the Chiefs and watched as a Stephen Donald-inspired home side tore Gatland's second stringers apart to post a 40-7 victory.
That match helped Gatland's thinking for the Lions tour and his decision to call in four Wales and two Scotland players has given him the flexibility to run two separate teams for the rest of their trip in New Zealand.
All six players are on the bench on Tuesday.
Despite that decision, Gatland has refused to accept he had split the touring party into a 'midweek' and 'test' team.
"There is no way we have divided into two," he said.
"I looked back at 2013 (in Australia) and between the first and third tests we made nine different selections.
"So for the players who might not be in the first test have to stay alive because they might get a chance in the second or third tests."
That possibility was also in the mind of Chiefs coach Dave Rennie who said he expected the Lions would be desperate to push their cases for test consideration against his team.
"They've got a number of guys who will be keen to play a bit of test footy on this tour and maybe it's a chance to scrap for some spots on the bench," he said.
"I'd imagine their test 15 will be nailed and probably stay in Auckland, so I think they've got a lot to play for."
Photo: PhotoSport Lions' Sean O'Brien is chased by Damian McKenzie.