SANTA CLARA, Calif. -- For San Francisco 49ers quarterback Jimmy Garoppolo, this offseason provided plenty of reasons to vent his frustrations with some salty language.

But when Garoppolo finally let one fly at the podium in the opening days of training camp, it had nothing to do with the trade up for quarterback Trey Lance or his status with the team. It had everything to do with how impressed he's been by veteran receiver Mohamed Sanu.

"He's looking f---ing good, man," Garoppolo said. "I mean, excuse the language, but he really is."

Of the many training camp platitudes thrown out this time of year, the "best shape of his life" trope reigns supreme. Whether that's true in Sanu's case is of little consequence. He's already earned his NFL bonafides over nine seasons with 4,694 receiving yards and 27 touchdowns.

The fact that Sanu is being talked about in such terms -- especially considering less than a year ago much of the football world had written him off as old, injury-plagued and, for lack of a better term, washed up -- is impressive.

Sanu is not only back with the 49ers for a second stint after 18 days with the team in 2020 but is already making a strong push to become the No. 3 wide receiver behind Deebo Samuel and Brandon Aiyuk in one of camp's most uncertain position battles.

Beyond Sanu, the battle for the third receiver job includes a mix of veterans such as Travis Benjamin, Richie James Jr. and unproven youngsters such as Jalen Hurd, Jauan Jennings, River Cracraft and Austin Watkins Jr.

Based on résumé, Sanu would be the obvious choice, but that's only true if he can get back to something closer to the player Kyle Shanahan coached as offensive coordinator for the Atlanta Falcons in 2016. Sanu caught 59 passes for 653 yards and four touchdowns that season as the No. 2 receiver behind Julio Jones on a team that reached the Super Bowl.

"He's in such a better spot," Shanahan said. "I think you ask our players and anybody who's watched him here, it looks like the guy I remember and not the guy that we had for that those week and a half or whatever it was ... hopefully he can keep it up and keep it going."

For the 49ers, who had three-plus receivers on the field the fifth-fewest times in the league in 2020, the third receiver spot doesn't look overly important on the surface.

But No. 3 wideout Kendrick Bourne led 49ers wideouts in receiving yards in 2018 and was second among all pass-catchers in 2020. That happened not only because Bourne had success working from the slot but also because he often found himself as the most durable and reliable wideout on the team.

Samuel missed nine games in 2020 because of injuries and Aiyuk missed four, leaving Bourne to pick up the slack. With Bourne now in New England, that job is open.

That Sanu seems to have emerged as the early favorite is a testament to his self-belief and the relationship he and Shanahan forged in Atlanta. Holding no grudges from the 49ers releasing him last year, Sanu had little doubt where he wanted to bounce back.

"I'm a football player and I have got common sense, too," Sanu said. "I'm a realist. I know if I was at my best and they cut me, I would have been like 'Damn.' But I wasn't. And I knew that so I was thinking I will get right and take advantage of the next opportunity."

As the free-agent market opened in March, Sanu was coming off what he called an "extensive" ankle surgery that cleaned up the remnants of the high ankle injury he suffered -- and made worse by trying to play through it -- with the Patriots in 2019.

The interest level in a 31-year-old receiver coming off ankle surgery and the second-least productive season of his career wasn't high. In his estimation, Sanu was closer to full health and had something to offer.

Sanu took matters into his own hands. He called Shanahan and explained he was healthy and could play a meaningful part in San Francisco. He also sent over videos so Shanahan could see for himself.

"I saw him last year when we had to let him go, which put some worry on it," Shanahan said. "But when a guy you know and a guy you respect calls you and you trust them, then you give [him] an opportunity. And he came in and he was everything he said."

In some ways, Sanu's return to San Francisco was fitting given that he was nearly a Niner during their Super Bowl run in 2019. At the time, the 49ers made a number of offers to acquire Sanu from the Falcons but they ultimately couldn't match the Patriots' offer of a second-round pick. San Francisco pivoted to a trade for Emmanuel Sanders instead.

Coincidentally, Sanu has drawn comparisons to Sanders for how quickly he's earned the respect of young receivers like Samuel and Aiyuk, both of whom expressed disappointment when Sanu was released last year. It's another role Sanu has embraced in his return.

"He teaches us the ins and outs of the game, not only just football but kind of like Emmanuel was when Emmanuel was here," Samuel said. "That's what we have here with Sanu. To me, it looked like he was the Sanu that he was when he was in Atlanta."

There is, of course, a long way to go before any roster or depth chart decisions must be made. Staying healthy will remain paramount for any receiver battling for a job on the Niners roster.

Until then, the competition will only intensify with younger options like Hurd attempting to prove themselves and push for prominent roles.

For Sanu, the competition isn't so much with his teammates as it is with proving to himself and, by proxy, the NFL world, that he has plenty of good football left.

"[If] somebody tells you what you can and can't do without them knowing who you are as a person, you as a competitor, it gives you a little fire," Sanu said. "And I'm excited for this opportunity I have now."