Barrett has a roving commission whichever jersey he wears, and the mercurial and brave McKenzie has the potential to do the same.
McKenzie's career has veered between first five-eighths and fullback but Gatland said returning veteran Aaron Cruden would go into the season as the preferred No. 10.
"I haven't really had a lot of conversation with Damian about it - (fullback) is probably where we see him at the moment, and potentially where he sees himself," Gatland told Radio Sport.
"There's no reason he couldn't move back to 10 in the future and we know he can cover us at first five.
"But long term there's definitely a position higher up in the All Blacks where he can probably cement a fullback spot.
"We know how dangerous he is bringing the ball back and in counter attacking, how brave he is, how good he is in the air. At the moment that's where we see him."
Gatland said McKenzie "took it easy in the pre-season" avoiding full contact.
"With a serious knee injury like that it takes a while to get up and running and get the joints moving again," said Gatland.
"He was a little bit stiff when he first started to train, and that's just the scar tissue and things.
"He's up fully training now, we'll try and give him some pre-season game time, and hopefully he's available for that opening game against the Blues."
Gatland said the Chiefs had been managing Jacobson's return.
"He's been settling back into a lot of conditioning work and started to do some contact work," he said.
"The aim for Luke is to come in for round three once he's got up to speed with all the fitness and contact work, when he feels comfortable.
"The most important thing is to get a full clearance from the medics. He looks sharp and is pretty excited, and looking really good."
Gatland told Foster the All Blacks have an open invitation to attend trainings and speak to the players. He sees promoting players into the test squad as an essential part of his job.
The Chiefs are sleeping in tents and sleeping bags this week, in preparation for Friday's pre-season game against the Blues in Waihi.
All Blacks will not be available but Gatland hopes some will line up in the Super Rugby opener at Eden Park on January 31.