"We're excited that Mitch is ready and it's an opportunity for him," Nagy said.
Foles didn't practice this week because of a hip injury. He originally went down during the fourth quarter of Chicago's Week 10 loss to the Minnesota Vikings and had to be carted off the field.
Nagy told reporters on Nov. 17 that Foles' injury wasn't "as bad as we once thought" and he was considered day-to-day heading into the team's bye last week.
Trubisky opened this season as Chicago's quarterback. The team went 3-0 in games that he started, but he was benched in the third quarter against the Atlanta Falcons in Week 3 after throwing an interception right to Blidi Wreh-Wilson.
Foles led the Bears to a 30-26 comeback win over the Falcons but has gone 2-5 in seven starts overall.
Trubisky threw for 560 yards with six touchdowns, three interceptions and a 59.3 completion percentage in his first three starts.
The Bears have lost four straight games heading into their matchup with the NFC North-leading Packers.