After a solid season with the Brooklyn Nets, Lonnie Walker IV was hoping to land a guaranteed contract this summer. He was confident he’d shown enough during his six-year NBA career that some team would view him as a desirable depth piece.

That didn’t happen.

Instead, the 25-year-old wing languished in free agency for nearly two full months, unable to find any club that would give him a permanent roster spot. Walker ultimately settled for an Exhibit 10 contract with the defending champion Celtics and arrived in Boston earlier this month.

An E-10 is little more than a training camp tryout. Walker is not part of Boston’s official 15-man roster, and his deal features no guaranteed money, outside of a nominal bonus he’d receive if he’s cut and plays a certain number of games for the Celtics’ G League affiliate.

What the Celtics were offering, though, was an opportunity to compete. And that was enough for Walker.

“Obviously, my free agency hasn’t gone as planned and whatnot,” Walker said Wednesday after the Celtics’ first training camp practice. “So, Brad Stevens, he’s given me the opportunity with the E-10 to kind of prove myself and show my capabilities offensively, defensively, off the court, being a great teammate. So I’m just really excited and grateful to be here, and I’m just going to work to the best of my capability.”

Walker isn’t your typical E-10 signee, having appeared in 322 games over the last six seasons with 88 starts. He played in 58 games off the bench for Brooklyn in 2023-24, shooting 38.4% from 3-point range. He averaged a career-high 20.1 points per 36 minutes as a Net — only three Celtics players averaged more last season — and has played especially well against Boston in his career, especially on the offensive end.

Scoring and 3-point shooting ability are Walker’s greatest assets (“I’ve always had it, since the womb,” he joked), but he knows he’ll need to prove he can impact the game in other ways in order to stick with the Celtics.

“I think everyone knows that I can score, my ability to do that,” the 6-foot-4 Miami product said. “But I think I do have really good — I’m athletic. I have the strength and the speed to play with the best of them. So I think this year, I really want to really lock in on that defensive side and kind of show everyone that I can play defense. If given, I could play my true position and go from there.”

Walker is one of just a handful of newcomers on a Celtics team that returned nearly its entire championship roster, but he does have prior connections to a few of his new teammates. He’s trained with Jrue Holiday in the offseason and played four seasons in San Antonio with Derrick White, whom Walker called “literally one of my closest friends.”

“That was my guy,” White said. “Got drafted a year after me, so we were kind of just a couple young guys trying to figure it out, learning under [Spurs coach Gregg Popovich]. He started in [the G League] his rookie year like I did, so we kind of had similar things. It’s always good to see him. Good guy, good energy around the gym and he can do a lot of special things on the court. It was good to see him and just get back to it.”

Walker is vying for the Celtics’ final open roster spot, which the team could choose to leave vacant entering the regular season. Head coach Joe Mazzulla said he’s taken the correct approach thus far.

“He’s patient,” Mazzulla said. “He understands the position he’s in, and he understands there will be plenty of opportunities for him to earn his position. He’s asked a lot of questions because he wants to understand. He’s willing to do what’s necessary to be the best of what we need.

“So as long as he has that … there’s plenty of opportunity there. The most important thing is, how does he fit into the dynamics of what we’re trying to accomplish on both ends of the floor, and can he execute the details?”

Walker figures to get plenty of run during the Celtics’ preseason, which tips off next Thursday against the Denver Nuggets in Abu Dhabi. The message he’s gotten from the team?

“I’ve got to earn it,” Walker said. “Obviously, there’s a lot of different aspects that might carry onto it, but being on an E-10, it’s not guaranteed. I’m not coming here with the mindset of, ‘OK, I’m on an E-10 and afterwards, I’m going to get the guaranteed contract.’ It’s like, I’ve got to work my tail off. I really have to, each and every day, put it all out on the court. First one in the gym, hopefully the last one out, come back later on, shoot and just be mentally and physically prepared for the outcome.”

Walker said Stevens, Boston’s president of basketball operations, also told him he might need to spend some time in the G League this season, something Walker hasn’t done since he was a Spurs rookie in 2018-19.

“And honestly, I’m perfectly fine with that,” he said. “Because as a man, you’ve got to take it on the chin. You’ve got to continue to work. You have to continue to be prepared and just keep being ready. I think I’m mentally prepared for almost any outcome that may pop up, and I know sooner or later that the worm will turn and that the light’s still at the end of the tunnel.”

Whether Walker can play his way out of the minor-league limbo and into a real role for the reigning champs will be one of the top storylines of Celtics camp.

“Obviously, he’s got a lot of talent,” Stevens said. “He’s done a lot of good things in the NBA, and we’ll see how it fits and plays itself out.”