SANTA CLARA, Calif. -- Although he has been a member of the San Francisco 49ers only since April, left tackle Trent Williams didn't hesitate when asked recently which of his new teammates he's most excited to see this season:

Running back Jerick McKinnon.

"The way he's looked in the offseason, I just can't fathom him not being a breakout player," Williams said.

Williams' sentiment is shared by the rest of the 49ers organization. McKinnon, affectionately referred to as "Jet," tore his right anterior cruciate ligament on Sept. 1, 2018, and his comeback has been nearly two excruciating years in the making. The 49ers signed McKinnon to a four-year, $30 million deal on March 14, 2018, after coach Kyle Shanahan targeted him as a potential focal point in his offense. But McKinnon has yet to appear in a regular-season game.

After suffering the injury and vowing to return in 2019, McKinnon's comeback halted last summer after he struggled to get his surgically repaired knee back to full strength. Almost exactly a year to the day after suffering the injury, the Niners put McKinnon on injured reserve, ending his season before it began for the second straight year. He had another procedure on the knee soon after and spent last season starting over on the long road to a return.

Suffice to say, the weight of the past two years has taken its toll on McKinnon.

"I could sit up here and say a thousand things, but the harsh reality of it is when something like that happens, you do have to go through those mental challenges and emotional challenges and things of that nature," McKinnon said. "So, for me it was about leaning on my faith, my loved ones. My teammates were always reaching out to me to make sure I was always in a good headspace, coaches reaching out to me, and to me, that was probably the thing that kept me going the most. ... I'm still new to the team and I haven't played in any games, so that was just a booster for me throughout the process, just making me go that much harder and then wanting to come back better than before."

Whether McKinnon, 28, will be able to reach pre-injury levels remains to be seen. The early returns are encouraging. He opened camp practicing without restriction and has authored at least one eye-opening run or catch in each of the early practices.

Shanahan coveted McKinnon's route-running and pass-catching ability despite what had been mostly modest production in his first four NFL seasons. He rushed for 570 yards and caught 51 passes for 421 yards with nine total touchdowns during his final season with the Minnesota Vikings in 2017 -- all career bests. At the time of McKinnon's initial injury, Shanahan said the loss of the running back meant seismic change in the plans for the offense that season.

In the past two seasons, the Niners have lacked a consistent pass-catching tailback. A healthy McKinnon could be just the X factor Shanahan needs for his offense to take the next step.

"We have so many weapons, so many guys that are versatile in the offense, but I do think I can open up a different element with my tool set and what I bring to the game," McKinnon said. "Kyle does a great job of putting players in the best situations to succeed. He's a matchup guru in matching guys up and playing to their strengths."

While running backs Raheem Mostert and Tevin Coleman figure to get the majority of the carries, it's not hard to envision McKinnon serving as a third-down specialist capable of lining up all over the formation and taking advantage of favorable matchups against bigger, slower defenders.

It's something the Niners haven't done much of in three years under Shanahan even though they've had some success when throwing to backs. While 49ers running backs averaged a league-leading 9.78 yards per reception in 2019, they were tied for 19th in the league in catches with 77 and were ninth in receiving yards (753).

Since Carlos Hyde had 59 catches for 350 yards in 2017, the Niners have not had a tailback finish a season with more than 27 receptions or 261 receiving yards. What's more, fullback Kyle Juszczyk has accounted for 30.4% of receptions and 37% of receiving yards among running backs on the 49ers over the past three years.

Which means McKinnon could carve out a substantial role.

"Watching the way he practices, how smooth he is, how he doesn't second-guess himself, how quickly he answers questions in meetings, all that kind of stuff, you would never guess that this guy hasn't been on the field for two years," Juszczyk said. "He just makes things look so natural. ... I think he's going to have a really good year."

In the offseason, McKinnon nearly became a salary-cap casualty because he was due to make $6.8 million in 2020. Instead, he agreed to take a sizable pay cut that would reward him for staying healthy and producing. Though he could have left to seek a bigger role with more touches, he wanted to deliver on the promise that he brought with him to the Bay Area.

Reworked contract in hand, McKinnon spent the offseason in Houston working out with Williams, receiver Deebo Samuel and Washington running back Adrian Peterson.

"Jet's even been through more and he hasn't been able to get on the field since he's been here as a Niner," Shanahan said. "I think everyone knows how hard that's been for him just emotionally and mentally."

Now that he's back healthy and involved, the hard part, according to Shanahan, is slowing down McKinnon and his two years of pent-up energy.

"It's kind of hard for me to tone back a little bit," McKinnon said. "I work like I'm broke so it's hard to stop working."