"That won't be happening before that game," Nagy said during a video call after the Bears practiced at Soldier Field.
Trubisky and Foles have been locked in a battle for the starting job throughout training camp, evenly rotating days on the first team since padded practices began Aug. 17.
Nagy, who confirmed the two will continue to split reps next week, declined to say who has the edge thus far.
"For us, we like where they are at, but that's an internal question for our coaches," Nagy said. "That's more gamesmanship than anything. But we know there can definitely be improvement for both of them. They are making good decisions. There are times they are making good throws. There are times they are making throws they'd like to have back.
"I'll put it this way: Intentionally, I'm not going to give you any direction right now."
In 2018, Nagy's first season as coach, the Bears went 12-4 as Trubisky passed for 3,223 yards, 24 touchdowns and 12 interceptions and rushed for 421 yards and three touchdowns.
Trubisky, while playing much of last season with a shoulder injury that required surgery in January, ranked 28th in the NFL in total QBR (39.4), tied for 27th in touchdown passes (17), 21st in passing yards (3,138), 32nd in yards gained per pass attempt (6.1) and 28th in traditional quarterback rating (83.0) as the Bears finished 8-8.
Chicago went out and traded for Foles -- the MVP of Super Bowl LII -- at the onset of the new league year. The Bears later declined Trubisky's fifth-year option and announced an open quarterback competition in training camp.
Neither quarterback tipped his hand Saturday.
"I'm not exactly sure [where it all stands]," said the 26-year-old Trubisky. "I think that'd be a good conversation to have with Coach probably Sunday, see how we did after the scrimmage, go back and watch some film and then have one more big week of practice before I would say they probably make a decision. But they really haven't told us where we're at or when the deadline is."
Added Foles: "I honestly haven't asked for any feedback. I just want to go out there and help this team, play out there, go execute these plays and help this offense and help this team in whatever role that may be. My focus is that."
Foles, 31, said the competition wasn't on his mind.
"I'm not even thinking about it," Foles said. "I'm just thinking about being the best player I can be for this team. With that, that's where the coaches know I stand. That's how I've been throughout my career. And so why would I change right now and all of a sudden let this thing overtake me?"