SANTA CLARA, Calif. -- San Francisco 49ers quarterback Jimmy Garoppolo is entering his sixth season in the league and second year of a five-year, $137.5 million contract.

Despite those two indisputable facts, nobody seems sure of what the 49ers have in Garoppolo. That's because Garoppolo, through his flashes of brilliance, moments of struggle and a devastating knee injury, simply hasn't done enough of the one thing that's most important when it comes to evaluating football players: play games.

Garoppolo, who has 10 career starts, enters an important year for his career and for the current and future state of the 49ers. This season is all about building a body of work from which he can truly be judged.

"[It's] very important," coach Kyle Shanahan said. "I was really looking forward to last year knowing that Jimmy hadn't played a lot of ball, but he had showed everyone the capability he has to be a very good quarterback and I was really looking forward to going through a whole year with him where we all knew he would have some ups and downs, but he had the ability and the mentality that you knew he would continue to climb. And he missed that year.

"That is what it is, and now he's done the work to be healthy, but Jimmy hasn't played a lot of football. Everyone knows he's a good player and knows he's talented, but we've got to go through some situations and go through playing the position. I'm just so pumped that he's healthy again."

When Garoppolo tore the anterior cruciate ligament in his left knee on Sept. 23, 2018, against the Kansas City Chiefs, it cost him the final 13 games of the season and essentially ended any hopes the Niners had of a surprise run to the postseason.

It was also the second time in as many opportunities that Garoppolo was unable to stay healthy when given the chance to start. Playing behind Tom Brady doesn't offer a lot of snaps for the backup, but Garoppolo made two starts in 2016 with the Patriots. He left the second start in the second quarter with a shoulder injury.

All of which helps explain one of Garoppolo's primary goals for this season.

"You want to be out there playing, especially at quarterback," Garoppolo said. "There's only one of you, so when you get that opportunity, you want to be the guy out there. I think taking it week by week, game by game and you can't look too far ahead, obviously, or you'll get yourself in trouble."

The fallout of Garoppolo's knee injury extended much deeper than another losing season. The Niners had rewarded Garoppolo largely based on a strong finish to the 2017 season in which he led them to five victories in his five starts after they started 1-10.

Little more than a month later, San Francisco made Garoppolo the league's highest-paid quarterback, a calculated gamble on what he would do in the future rather than what he'd accomplished. In the process, the Niners tossed away Shanahan and general manager John Lynch's initial plan to pursue free-agent quarterback Kirk Cousins.

Garoppolo was their guy. They believed any growing pains he suffered in 2018, his first full year as a starter, would set him up for success in 2019.

Those plans never came to fruition, though, as Garoppolo's decision to try for an extra couple of yards against the Chiefs derailed that strategy. It also left open the question of whether Garoppolo can truly become the franchise quarterback.

This preseason and training camp have provided a handful of chances for Garoppolo to ride that roller coaster. Teammates have noticed an increased urgency in him during the offseason and throughout this camp.

"There does seem to be something there to prove," fullback Kyle Juszczyk said. "He's not one that, you know, talks about it a lot: I need to do this. I need to prove this. But you can just see in the way he conducts himself that this means a lot to him. He puts in a ton of time, a ton of effort. And you can feel that energy from him."

Much was made of the mid-August practice in which he threw interceptions on five consecutive pass attempts, which was compounded five days later, when he posted a 0.0 passer rating against the Denver Broncos in the second preseason game.

Garoppolo also had his share of successes. Most important, he never seemed to have lingering issues with his knee -- at least not the physical kind -- and he was sharp in more practices than not. He also rebounded from the rough week in Denver with a 116.2 passer rating against the Chiefs in the third preseason game.

Suffice to say, the discussion surrounding Garoppolo is different now than it was entering the 2018 season.

"It's crazy what a year can do," Garoppolo said. "I have so much motivation in myself and I push myself so much that that's all I need. All the noise on the outside, you kind of just tune it out."

For better or worse, that noise figures to get louder this season. Garoppolo's massive contract has been surpassed by those of a handful of more accomplished quarterbacks, though his cap number for 2019 is a reasonable $19.35 million.

That number will spike significantly in 2020, when it jumps to $26 million, and the Niners could have a decision to make. While it's unlikely things will go poorly enough for them to move on from Garoppolo after this season, another serious injury would force them to at least consider their options. That's especially true considering all of Garoppolo's guarantees will be paid out by the end of this season.

The Niners could move on from Garoppolo with the remaining $4.2 million of his prorated $7 million signing bonus counting against their 2020 cap.

Of course, if things go the way the team and Garoppolo hope and he plays well for an extended period, none of that will matter and he will emerge from this season as a proven commodity who still figures prominently into the Niners' long-term plans.

"We've got high aspirations for this team," Lynch said. "And he's obviously a big part of that. But we've got a lot of belief that he's going to answer the bell."