49ers' Javon Kinlaw remains a work in progress to replace DeForest Buckner

Javon Kinlaw's NFL draft profile (0:43)

Check out some the highlights that make former South Carolina defensive tackle Javon Kinlaw a top prospect in this year's NFL draft. (0:43)

SANTA CLARA, Calif. -- In the days after trading defensive tackle DeForest Buckner to the Indianapolis Colts, San Francisco 49ers general manager John Lynch repeatedly called the move the most difficult thing he's had to make during his three-plus years on the job.

If that sounded like hyperbole, it wasn't. Months later, Lynch brought it up again.

"We did not take that lightly," Lynch said of trading Buckner. "I think we exhausted everything that we could to try to not make that happen. But at the end of the day, we had to look at what we could do to keep our team together, you know, not just one player, even though that one player represented so much of what we wanted to be."

Trading Buckner was painstaking, but the Niners viewed it as a necessary move in order to keep other pieces in place. They used the money saved to retain defensive lineman Arik Armstead and free safety Jimmie Ward, among others. They used the draft pick acquired in the trade for Buckner to land his replacement, Javon Kinlaw, in the first round after a trade down that later helped them move up for receiver Brandon Aiyuk.

The logic behind the move was sound. But Kinlaw remains a work in progress, and Buckner's absence has hit even harder during a season in which most of the team's best players have been lost to injury. Buckner's ability to stay on the field -- he's missed just one game out of a possible 76 in nearly five seasons in the league -- might be the thing the 49ers miss most. Replacing him hasn't been as easy as just turning to their bevy of talented defensive linemen or as simple as installing Kinlaw in his place.

The initial plan to replace Buckner was to have Solomon Thomas move inside to the vacated three-technique defensive tackle spot. The hope was that Thomas playing at his more natural position during the final year of his contract would finally ignite his career. Those hopes were dashed when Thomas suffered a torn ACL in Week 2.

Suddenly, Kinlaw, who was supposed to be eased in, was tossed into the deep end and told to learn how to swim. The results have been mixed. There have been the occasional flashes -- Kinlaw is tied for 13th among all defensive tackle in run stops, and his 9.4% pass-rush win rate is 20th among defensive tackles -- but there have also been plenty of hiccups.

Kinlaw has just 1.5 sacks, which didn't come until Week 10, and he's struggled mightily against double-teams, winning his rush on 4 of 76 pass-rush reps against multiple blockers. Even when he's seen one-on-one matchups, Kinlaw has struggled to identify play-action passes and quickly convert from defending the run to getting after the quarterback.

To 49ers defensive coordinator Robert Saleh, Kinlaw's struggles to get sacks have occasionally reminded him of Buckner's three-sack 2017 season, when he would have chances but come up a step short more often than not.

"When he does get his one-on-ones, he does have to win," Saleh said. "He has had some wins. ... He's had his opportunities and those are things that he's going to learn. It's the same thing that happened with Buck, where we talked about he needs to find that one step. I feel like that's where Kinlaw is with regards to, he's had some opportunities, he's missing a step and that just comes with time and reps and learning. I believe that he's going to get all that. He is just hungry for knowledge and just constantly trying to learn from everything. So, I believe that he's a guy that won't fail."

Fair or not, the comparison to Buckner isn't likely to go away anytime soon. Still, the Niners remain resolute that when Kinlaw puts it all together, he's going to be a force. Before he finally got his first sack against New Orleans on Nov. 15, nose tackle D.J. Jones said he believed once Kinlaw got it, he would take off and "there won't be a ceiling for him."

Those beliefs have been reinforced by more than just Kinlaw's ability to get close. Kinlaw has impressed coach Kyle Shanahan with how he's carried himself and learned to do the extra things to take care of his body after practice. Saleh also points to Kinlaw's ability to recognize the small details that lead to mistakes and work to correct them.

That's something Kinlaw hasn't been shy about in discussing his rookie season, either. Back in training camp, Kinlaw called himself out multiple times for playing with his pads too high and bemoaning his need to refine his approach.

He's still working on it.

"I'm not really worried about sacking the QB," Kinlaw said. "I'm just worried about getting a win. And, of course, still trying to learn how to play good technique. The sacks, they're going to come. They're always going to come, but right now I'm still in the phase of trying to play with good technique and play good football."