The Bears turned to backup Chase Daniel, who entered Sunday's game and promptly turned the ball over on downs.
Nagy said after the game that Trubisky "didn't look right."
Nagy also spoke about the decision to remove Trubisky from the game, per Bergman:
"It was all based off he wasn't feeling right. His hip was hurting him. We knew a few series earlier that something wasn't right. We watched him to keep an eye on him and see how it was. I had to go on the side and talk to him. ... He needed to be honest with us and trying to play through that is what he was doing. ... I appreciate Mitch's toughness. The kid did not want to come out."
On Monday, Nagy told reporters Trubisky "absolutely" will remain the Bears' starter when healthy and that the decision to go to Daniel had "zero to do" with Trubisky's play.
The third-year signal-caller has been bothered by injuries in each of the last two seasons. He missed two games in 2018 because of a shoulder injury. According to Adam Schefter of ESPN, he then suffered a dislocated left shoulder with a slight labrum tear in Week 4, which sidelined him for one game.
While he has dealt with his shoulder injury, Trubisky entered play Sunday completing 63.6 percent of his passes for 1,390 yards, eight touchdowns and three interceptions.
Nagy said in September that he felt "comfortable" with Daniel under center, noting the veteran "knows the offense really, really well."