Column: Justin Fields will see plenty of action in the Chicago Bears preseason opener Saturday. But when will the rookie quarterback be ready to start?

Matt Nagy is as excited as the Chicago Bears fan base about the debut of rookie quarterback Justin Fields — aka the franchise savior — in the preseason opener Saturday against the Miami Dolphins at Soldier Field.

The game only will amplify the question everyone has been asking for months: Is there a path for Fields to be the starter when the season kicks off Sept. 12 against the Los Angeles Rams in Inglewood, Calif.?

Veteran Andy Dalton, who according to Nagy has aced the test of mastering the offense, will start against the Dolphins and is expected to play briefly. Fields will enter, likely getting some snaps with the starting line and some top-tier skill-position players, and he’s expected to get extended playing time. Whether that means the rest of the first half and into the second half, we’ll have to see. But it’s apparent the preseason is about Fields, and the Bears are going to get a long look at him.

“There’s a bunch of different experiences for these quarterbacks,” Nagy said, referencing how training camp visitor Doug Pederson was the starter for Andy Reid with the Philadelphia Eagles in 1999 while first-round pick Donovan McNabb spent time on the bench. “A lot of different levels of where they’re at, when they’re ready, when they’re not ready, where’s the team at. So we try to use them all and understand, are there great examples of quarterbacks sitting for a few years and learning and becoming Hall of Fame quarterbacks? Absolutely.

“Are there similar examples of guys coming in and playing from the very first snap and being great quarterbacks? For sure. So we just want to make it ours on what we think is right for Justin and for our team in the long run. That’s the evaluation part. And history gives you examples of situations that can help you get through some of those times, day by day.”

Nagy was with Reid with the Kansas City Chiefs when Patrick Mahomes was on the bench for the first 15 games in 2017 behind Alex Smith, who visited training camp Thursday at Halas Hall for the Bears’ practice with the Dolphins. Smith was the No. 1 pick in 2005, and his first start with the San Francisco 49ers came in Week 5. He struggled as a rookie, and his career didn’t take off until Year 7.

“There’s all different ways of doing it,” Dalton said. “I was fortunate that I was able to play as a rookie (in 2011 with the Cincinnati Bengals). Aaron (Rodgers) didn’t get to play his rookie year. Mahomes, he didn’t play his rookie year. But then there’s other guys that’ll just step in right away.”

A ton of factors are involved in the decision, and it’s evident Fields is competing against himself more than anything else. When Fields is ready to play, chances are his number will be called — unless Dalton is playing out of his mind and the offense is clicking at a high level.

That’s what makes an extended opportunity to evaluate Fields in the preseason so important. Finally, Nagy and his assistants will have something more tangible than training camp practice film to evaluate. They’ll be able to weigh the playmaking ability, like when Fields faked a handoff, rolled out to the right and then threw a bomb across the field to streaking wide receiver Jon’Vea Johnson for a touchdown Wednesday.

Those plays need to be balanced against the natural rookie errors that are going to pop up. One of those occurred a little before the deep shot to Johnson when Fields appeared to make a poor read, throwing a pass to a spot he didn’t have a receiver, leading to an easy interception by backup Dolphins cornerback Javaris Davis.

Dalton is going to get only a few snaps in Saturday’s game, but Fields will play a lot. The coaches have professed to have a comfort level in the veteran, and that’s no small factor in the big picture when you consider Nagy is under contract through 2022 and is feeling pressure to have success this season.

Nagy cited Dalton’s proficiency with the offense, saying the first mental mistake of training camp didn’t come until Tuesday, when he forgot to send a wide receiver in motion before the snap.

“When they told me that was my first mental error, I said, ‘Well, I expect to not have any of them. It’s one too many,’ ” Dalton said.

Fields has proved he can call plays in the huddle — an assignment he was given at the end of the offseason program — and the preseason will provide a glimpse into how he has prepared to make line checks and identify coverages pre-snap and post-snap.

If the Bears had more questions about Dalton, Nagy said he would be in line for more playing time against the Dolphins. After the fact, Nagy said the decision to sit starters throughout the 2019 preseason was a mistake.

“(Dalton) could play tomorrow in a (regular-season) game and I would feel great about it,” Nagy said. “Our players would feel great about it. That’s probably why he’ll play less snaps. If we go out there and score a touchdown on the first drive, I can promise you, if it’s three plays, he’s out. But if we want to see more and he feels like he needs more, too, we’ll do that. It’ll be a chance for us to talk through it. And again, we need to evaluate Justin, so we’re going to want to see him do some stuff.”

What Fields does with his opportunity against the Dolphins, good or bad, surely will affect the ongoing discussion about when he’ll ascend to a starting role.

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