Coach Matt Nagy said on Friday he would make a game-time decision between Fields and veteran Andy Dalton, but the team downgraded Dalton to doubtful because of a bone bruise in his left knee.
Fields -- selected No. 11 overall in the NFL draft -- is looking to bounce back after Chicago's disastrous 26-6 loss to the Cleveland Browns last week.
"This week's practice compared to last week's practice, I felt just more comfortable at practice just kind of getting that under my belt and getting kind of past that," he said. "Last week, you really can't get worse than that. I mean, I hope not. But I felt comfortable this week."
Cleveland sacked Fields nine times in the rookie's NFL starting debut and held him to just 6 of 20 passing for 68 yards and 12 rushing yards on three attempts.
Fields also suffered a right thumb injury in the Browns game, but ended up having full participation in practice all week and did not appear on the final report with an injury designation.
"Justin's game that he played last week, he did a lot of things that he's going to learn from," Nagy said. "But we also, and myself, have to help him. I think the biggest thing for him is, 'OK, here's how I was in the week of practice. Here's how I was on game day, both physically and mentally. Now how am I going to be heading into this week? Am I getting better? Is there improvement? Am I getting better at the things I was good at? Am I getting better at the things that I wasn't so good at?'
"And that's what we're doing as coaches throughout the week of practice, is being able to watch him and see that. I can say from last week to this week that you do see that advancement. That there, knowing and feeling how he practiced, is why I would answer it that way."
Nagy has repeatedly insisted that Dalton is the Bears' starting quarterback when healthy, but the 33-year-old is clearly still limited by the knee injury he suffered in Week 2 against the Cincinnati Bengals.
"I feel good," Dalton said Friday. "When you suffer an injury, you're trying to do everything you can to rehab and get feeling good as soon as possible. So everything's been heading in the right direction and everything's improving so I feel good about where I'm at."