Shortly after the Steelers released him in late July, Shawn Lemon began attacking his iPhone with intensity.

He had compiled contacts for the personnel departments of all 32 NFL teams and the well-traveled, often-rejected outside linebacker was, again, unemployed and undaunted.

Some teams responded to Lemon’s “Will you give me a job?” request with a question: Why isn’t your agent making this call for you?

They obviously didn’t know that resourcefulness was part of Lemon’s resume. After all, Lemon had convinced his agent, David Canter, to represent him in 2012 by making a phone call. So back to those conversations with NFL teams …

“I said ‘My agent’s working as well,’” Lemon said. “I mean, I was going to do everything within my power to help myself. No one will work for you like you will work for you. People might think you’re crazy, but if you want something that bad in life, you’ll do whatever you have to do to get it.”

Lemon, 26, who was signed by the 49ers last week, has endured plenty to improbably reach this stage: On Saturday, one trade, three leagues, five teams, five releases and eight teams after he left the University of Akron, he finally could play an NFL snap when the 49ers visit Houston in their preseason opener.

Considering his three-province, four-state odyssey, his NFL debut will be a feel-good moment. But more rejection is certainly in store. Lemon was signed to fill the roster spot created when the 49ers released Aldon Smith, but the outside-linebacker corps is still well-stocked with Ahmad Brooks and three recent draft picks: rookie Eli Harold, Aaron Lynch and Corey Lemonier.

On Thursday, Lemon was told no one expected him to survive the summer. No one thinks he’ll make the 53-man roster. He smiled.

“And no one — besides my parents — expected me to get a Division I scholarship,” Lemon said. “No one expected me to be in professional football. I’ve been told I couldn’t do something my whole life. I embrace that.”

Evidently.

Consider his first 12 months in professional football when Lemon was routinely told he couldn’t play. It began in 2011 when he signed with the Canadian Football League’s Winnipeg Blue Bombers on July 18.

He was released July 21.

What happened? “That was the weirdest thing ever,” Lemon said. “They signed me, but then they decided they wanted an older player. So after they brought me up, they just released me.”

And so it began. Lemon spent five weeks with Saskatchewan (released) before sliding a rung down football’s food chain to the $500-a-week Arena Football League. He spent five weeks with the SaberCats (traded) and three weeks with the Orlando Predators (released) before, again, moving even further from the NFL: He left Orlando and signed with the Sioux Falls Storm of the Indoor Football League.

In three games with the Storm, he had 10 tackles (seven solo) and two sacks. He sent a video to the Edmonton Eskimos and his play inspired a contact offer.

Lemon, 6-foot-2 and 250 pounds, arrived for his second CFL stint with more weight and less selfishness. He admits his lone goal in previous stops was to get glory.

“I didn’t have a big-scheme mind-set,” Lemon said. “I didn’t understand that every play is not designed for you to get a sack. It was about learning to play within a scheme and growing as a player.”

After a six-sack season in 2012, Lemon was released, but finally found a home in Calgary. He was limited by a hamstring injury in 2013 before thriving with the Stampeders last year. Lemon had 14 sacks and tied a CFL record with eight forced fumbles to lead Calgary to the Grey Cup title.

His breakthrough brought long-awaited attention. He visited 14 NFL teams before signing in January with Pittsburgh, where the good times lasted six months: The Steelers released him July 28, partly because a strained Achilles tendon sidelined him for the start of training camp.

Lemon insists he has been allergic to discouragement during his career, but acknowledged that his release from the Steelers made him wonder if he’d get another chance. On Aug. 1, a few days after he returned home to Maryland, he made an 80-minute solo drive to see Washington’s training-camp practice in Richmond, Va.

“It was a sick feeling being on the other side of that fence,” Lemon said. “I wasn’t in the NFL and now I’m a fan. It felt so bad for a moment, but then I felt motivated. It was like ‘No, I’ve got to get back.’”

Lemon is back in the game, but it’s certainly possible this will be the end of the road for an NFL rookie who will turn 27 on Aug. 25. Not surprisingly, the man who already has beaten long odds on an improbable journey is undeterred.

“If there’s something you want in life, put your all into it,” he said. “No matter how many doors close — kick open the next one.”

Eric Branch is a San Francisco Chronicle staff writer. E-mail: ebranch@sfchronicle.com Twitter: @Eric_Branch