"It wasn't as bad as we once thought," Nagy said of the injury he described as being a combination of a strain and a bruise to the quarterback's hip/glute area.
A source told ESPN's Adam Schefter that the initial diagnosis was a hip pointer and that Foles was scheduled for more tests on Tuesday.
Nagy said he doesn't think Foles will need to go on injured reserve, but he did leave the door open to a possible change at quarterback when the Bears come off their bye week.
"When you lose four games in a row, it's all on the table. Everything's out there," Nagy said. "The No. 1 thing with Nick and with Mitch [Trubisky] that we are concerned with right now is to make sure their health is the No. 1 priority. "
Trubisky, who began the season as Chicago's starting quarterback before losing the job to Foles, has missed two straight weeks after suffering a shoulder injury while making a brief appearance in an overtime loss to the Saints in Week 8.
"They're both a little banged up, that's the No. 1 thing we have to look at," Nagy said of his quarterbacks. "We'll take this bye week here and we'll self-scout ourselves, and we'll see the wheres and the whys. And whatever we need to do, we'll do in a lot of different areas."
The Bears next play Week 12 against the rival Green Bay Packers. Nagy said he expects offensive coordinator Bill Lazor to remain the playcaller when they return after the bye.