Audi and BMW are expected to decide which of their drivers will take part in the joint-race with SUPER GT by the end of the DTM season.
Between six and 10 DTM cars will head to Fuji for the 'SUPER GT x DTM Dream Race' that will be held on November 22-24, with the field size dictated by logistical costs for the DTM.
Audi, BMW and the R-Motorsport Aston Martin brand will all be represented in the Fuji race after Nissan, Lexus and Toyota make cameos in the DTM's Hockenheim finale (October 4-6) to help set the Balance of Performance for the joint-race.
Audi motorsport boss Dieter Gass told Autosport that Robin Frijns will not take part in the combined race due to a clash with ABB FIA Formula E's season-opening Saudi Arabia races.
"It's not an easy one," said Gass. "Because it's parallel to the season opener in Formula E, [which] means the only thing known is Robin won't drive and that's a tick in the box!
"Everything else, we need to see how the season pans out and then make further plans."
Gass also said that the DTM had held discussions over having multiple drivers share the running at Fuji, but he explained that the difficulties in accommodating each driver's set-up - as well as the complication in explaining the rotation to TV audiences - meant such a scenario was unlikely.
Regarding BMW's line-up at Fuji, the marque's motorsport director Jens Marquardt told Autosport: "[We'll] just leave it open a bit for the time being. Just really focus on the championship.
"And then at a later stage, we really go and decide as to how the package [for the joint-race] will look.
"For us, it is really important that we focus on each [2019 DTM] event. We've seen it [at Brands Hatch] - every race is difficult - the weather plays a factor, having the strategy right.
"In that respect, the best way is to say 'hey guys, let's focus on the events here first'.
"Then at some stage think about what we do because it's still the middle of November [for the Fuji race] - there's still some time to go."
While the R-Motorsport Aston squad does not have the same resource level as Audi and BMW, it will have a presence at Fuji.
Team principal Florian Kamelger confirmed to Autosport its timeline for making a driver decision for Fuji, saying: "The decision hasn't been taken yet.
"We have to decide in the next couple of weeks, and the moment I know I'll tell you."