Andrew Luck discusses his return to the football field and how he's having more fun playing football now than he did before. (1:39)

INDIANAPOLIS -- Even Andrew Luck wondered at times if he would ever play football again.

That's understandable when you think about what Luck has endured over the past 19 months. Right shoulder surgery. Cortisone shots. Feeling helpless because he believed he let the Indianapolis Colts down by missing all of last season. A six-week trip to the Netherlands to rehab his shoulder and to try to clear his head. Working with throwing experts in Southern California with one goal in mind: being the quarterback he once was.

The Colts' franchise quarterback is back on the field, with the fate of the once-proud franchise resting on the health of his surgically repaired right shoulder. But everybody still wants to know if Luck, who turns 29 in September, can get back -- all the way back -- to being elite. A quarterback who, during his first three years in the NFL, was already being labeled as one of the league's best. A quarterback who could make undrafted players look like serviceable NFL players, average players look good and good players look like Pro Bowlers.

With his shoulder injury hopefully behind him, Andrew Luck has looked great in training camp. "I didn't know if I'd ever have this much fun practicing and playing football," he said. AP Photo/Elaine Thompson

"Nobody knows what's going to happen," ESPN NFL analyst Louis Riddick said. "It's hard to judge another man's resolve. His willingness to repeat the same kind of punishment that he did before. You don't know how he's going to be until the regular season and people are gunning for him and throwing everything but the kitchen sink at him to try to put him on the ground every single snap. You just don't know."

Luck will look to take another step in his recovery Monday at 8 p.m. ET (ESPN), when he's expected to play into the second quarter against the Baltimore Ravens. It's expected that he'll play through at least halftime in the third preseason game, on Saturday against San Francisco (4:30 p.m. ET).

Physically, Luck has passed every test. He has been a full participant in each training camp practice with the exception of three planned days when he did everything except throw a football. Luck is a refreshed person. He looks, talks and keeps a smile on his face like a 5-year-old on Christmas morning. That wasn't the case at this time last year, when nobody had any idea when he would throw, let alone play in a game.

Andrew Luck's Injury Timeline For nearly three years, the Colts QB has been playing through or dealing with injuries. Here's a look at his journey: Sept. 27, 2015: He injures his throwing shoulder in a win against Tennessee

Nov. 8, 2015: A lacerated kidney in Week 9 eventually ends his season

2016 season: He plays despite an ailing shoulder, missing one game (concussion)

Jan. 19, 2017: He has shoulder surgery, is expected to be ready for 2017 season

April 17, 2017: He admits his shoulder injury occurred in 2015

2017 season: The Colts wait for him, but he misses the entire 2017 season

November, 2017: He travels to Europe seeking treatment for his shoulder

June 12, 2018: He throws for the first time since October of 2017

July 20, 2018: He is officially cleared for full participation in training camp

Aug. 7, 2018: He says he wasn't sure he would play football again

Aug. 9, 2018: He gets hit in a game for first time since 2016

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"You can see why he was the player that he was at Stanford, the No. 1 pick coming out and the player that he's been in the NFL, because it doesn't look like this everywhere," offensive coordinator Nick Sirianni said. "I know that. There's not a lot of teams that can come out and practice and be like, 'Man, we are just better because he's on the field.'"

Luck, admittedly, needs to find the comfort zone of making deep throws, a strength throughout his career. And he needs to see how his shoulder reacts after being hit or sacked numerous times and making 35-40 throws in a game. Does it become a mental game in which Luck wonders how he'll handle taking a pounding again? That's what happens when you have been sacked 156 times in addition to everything Luck has had to deal with over the past three years -- the missed playing time, missed practice time and frustration of wondering if he would play again.

New Orleans Saints quarterback Drew Brees, who had shoulder surgery in 2006, talked with Luck before the start of last season, and several times since, about the obstacles in the recovery process. Brees tore the labrum in his right shoulder in the final game of the 2005 season. He threw for 4,418 yards and 26 touchdowns while starting all 16 games the following season.

"It's a tough deal, because if you haven't gone through that before -- especially an injury to your throwing shoulder -- you're unsure what every little feeling is, right? And at some point, I think you just have to trust when you can, like, push through and just the process by which you get to the point where you are competing again," Brees said. "And it's a long process. It's a long, hard process. And it's as much up here [pointing to his head] as it is just the physical nature of fighting through that rehab. Andrew's a bright guy, he's a tough guy, and ... a guy who wants to be available for his team and be around it."

Luck has routinely been lauded for his toughness and competitiveness. He never has had a problem holding on to the ball for an extra second to make a throw or attempt to run over a linebacker to get the first down, because he's built like a linebacker.

That has to change.

Luck has to realize there's nothing wrong with throwing the ball away, sliding or going out of bounds to avoid taking an unnecessary hit to help his career longevity. He's no longer indestructible.

The impact of Andrew Luck's return has rippled through the organization: "There's not a lot of teams that can come out and practice and be like, 'Man, we are just better because he's on the field,'" Colts offensive coordinator Nick Sirianni said. Otto Greule Jr/Getty Images

The Colts know anything can happen with Luck. That's why they're adamant they won't trade Jacoby Brissett, who started 15 games last season and is capable of stepping in if necessary. Not even for a first-round pick.

"[Luck] can't go through that again," Riddick said. "It's not a matter of him wanting to. He just can't, and you hope he's smart [enough] to say, 'Look, I've taken enough for the team as far as getting my ass kicked out here trying to win games. If I want to last in this league another seven to nine years, I can't play the way I've played in the past.' So I would assume that's what it's going to come down to on his part instead of the fundamental shift. I think it's going to be more of a choice for him."

Luck did not miss a meaningful snap during his first three seasons. He aimed to do the same thing after the string of injuries started in Week 3 of the 2015 season. The Colts had Luck sitting out practices at least one day a week and limited at other times, but there was only so much they could do before the shoulder, ribs and lacerated kidney injuries caused him to miss 26 games over the past three seasons.

"Nobody knows what's going to happen. It's hard to judge another man's resolve." ESPN analyst Louis Riddick on Andrew Luck's return to the lineup

"Think about how long he's been playing," ESPN medical expert Stephania Bell said. "It's been part of his life every day. But then all of a sudden he couldn't do this thing the same way he's done it at an elite level. It's natural to have some apprehension on whether you can really return to that prior level of performance. Not to mention, it's no secret, all the expectations. Media are asking, fans are asking. It's not like you can go into a vacuum."

How soon Luck returns to his old self -- if he does at all -- is anybody's guess. The Colts have spent the past 19 months taking a meticulous approach in his return, all the way down to how many days he would throw in training camp practice. Luck played in his first game since Week 17 of the 2016 season, on Aug. 9 against the Seattle Seahawks. It was only two series, but it calmed some nerves, because he was on the field throwing passes and even getting hit again.

"I didn't know if I'd ever have this much fun practicing and playing football," Luck said. "I sort of decided that what I felt, I was going to feel. I didn't feel like I had to be in charge. I think I took the pressure off myself. And I'm sure there will be some other times when there are those rushes of emotion."

It's easy to forget how good Luck was when he was healthy. A quick "Andrew Luck" search on YouTube refreshes your memory. That search turns up Luck's three straight 11-5 seasons, including reaching the AFC Championship Game in 2014, and 12 game-winning drives in the fourth quarter and overtime during that span. Colts general manager Chris Ballard still cringes -- and then smiles -- when he thinks about watching Luck lead the Colts from 28 points down in the third quarter to a playoff victory against the Chiefs in January 2014 when Ballard was in Kansas City's front office.

Luck did those things with a flawed roster around him.

Receiver Ryan Grant, who is in his first season with the Colts, compared playing with Luck to when the late 2Pac teamed up with Grammy Award-winning producer Dr. Dre. Luck, like Dr. Dre, makes you a better player. Brees has already proclaimed Luck will win Comeback Player of the Year.

"Everyone knew Andrew Luck was a dominant quarterback," said tight end Eric Ebron, who is in his first season with the Colts. "He's always made his receivers look good, and his receivers have made him look good. Andrew has always been a force, and you just love that. Now that I'm out here playing with him, you see why. He knows everything. Reads coverages great. Very easy to get on the same page with him."

Indianapolis is in a rebuilding mode with Ballard orchestrating a youth movement. They have two starters, both on offense, remaining from Luck's last healthy season in 2014. The Colts took their lumps without Luck last season (4-12), and they know their chances of speeding up the rebuilding process improve significantly if he's healthy and effective.

"He makes everyone better around him," Sirianni said. "I think of it like you're Kobe Bryant, LeBron James in basketball. They're at the top of the John Wooden Pyramid of Success. The top of it is competitive greatness. Not only do you rise to the occasion, you pull everybody else up to it. You make everybody else's game better. That's what Andrew does."