Nagy told reporters Monday that veteran Andy Dalton and Justin Fields also are being considered, but they need to be evaluated throughout the week because of recent injuries.
Dalton and Fields were expected to battle for the Bears' starting quarterback role throughout the season. Foles did not take a snap through the first three weeks and was expected to serve as a backup.
"All three are under consideration right now in regard to where they're at, so we'll just kind of have to see in the next couple days where they're all at," Nagy said.
"We know where Nick's at, health-wise [not injured], but we just want to keep an eye on Justin and Andy," he said.
Dalton started the season atop the depth chart. Fields earned his first career start in Week when Dalton bruised his knee in Week 2.
Foles joined the team through a 2020 trade with the Jacksonville Jaguars and started seven games last season.
Fields sustained an injury to his right throwing hand during the Bears' loss to the Cleveland Browns on Sunday in Cleveland. He completed just 6 of 20 passes for 68 yards and was sacked nine times in the 26-6 setback.
"I think [Fields] learned a lot through the week of practice that we had," Nagy said. "I think he got better every day. And again, one of the things that we talked about for him moving through this process that he's going to go through is that there are going to be highs and lows."
The Bears will host the Lions at 1 p.m. EDT Sunday at Soldier Field in Chicago. The Lions are tied for allowing the fifth-most passing touchdowns (seven) and intercepted one pass through the first three weeks of the season.
They allowed a league-high 123.2 quarterback rating to opposing passers. Their 46.4% first down percentage is the second-worst clip in the NFL and leads the NFC.