The tiny tissue grafts inside Marcus Lattimore’s right knee are what will determine, above all else, if he is ever an elite running back again.

Yet in the six months, to the day, between his serious knee injury in a game against Tennessee and Saturday, when he was drafted in the fourth round by the San Francisco 49ers, his seemingly unwavering optimism played no small role in him moving past the scar on the front of his knee.

His positive outlook during hours of rehabilitation leading up to the NFL draft came from his own personality, to be sure, but also from outside influences he sought, and those who found him in the days after a gruesome scene in which he dislocated his knee and tore three of its four major ligaments: the anterior cruciate, lateral collateral and posterior cruciate.

Lattimore, a former South Carolina running back, leaned on friends who visited him and his strong Christian faith — both of which have always been linchpins of his life. But there were also new voices of hope, like NFL running backs Willis McGahee and Frank Gore. Lattimore had never met either. But they both knew him, in a way. They spoke with him on the phone in his dark days after the injury, when he wondered if he would ever be the same player again.

“Right after it happened, I doubted myself,” Lattimore said. “I did do that, and I lost hope.”

Lattimore went 30 spots behind USC wide receiver Ace Sanders (Jacksonville) and one spot ahead of defensive end Devin Taylor (Detroit). Two rounds later, outside linebacker DeVonte Holloman went to Dallas with the sixth round’s 17th pick. Center T.J. Johnson was picked by Cincinnati with the draft’s fourth-to-last selection. Tight end Justice Cunningham went last overall.

The Clemson players selected Saturday were defensive end Malliciah Goodman (fourth round, Atlanta); safety Jonathan Meeks (fifth, Buffalo); and running back and former Berkeley High standout Andre Ellington (sixth, Arizona).

McGahee tore three knee ligaments in his final college game at Miami, but has run for 8,097 yards and 63 touchdowns in nine NFL seasons. Gore, who also played at Miami, tore his left ACL in 2002 and his right ACL in 2003. A third-round pick in 2005, he has 8,839 yards and 51 touchdowns, and has made the Pro Bowl four times.

“Those guys are all inspirations to me because of what they’ve been through and how they came through it,” Lattimore said on a teleconference.

“(Gore) just told me to keep that positive mindset, and that’s what I’ve been doing these past five, six months. I feel like that’s why I’m doing so great with my rehab.”

Lattimore can thank Gore in person for his guidance, because they will be teammates in San Francisco, on a team that made the NFC championship game two years ago and the Super Bowl last season.

The 49ers are plenty deep at running back, with Kendall Hunter and LaMichael James backing up the 29-year-old Gore, after being drafted in 2011 and 2012. Lattimore has expressed hope that he could play next season, but the 49ers obviously don’t need him to.

“We’re not going to put him on the field until he’s 100 percent, and that may not be this year,” said San Francisco coach Jim Harbaugh.

But Harbaugh is excited about Lattimore’s eagerness and talent. If not for last season’s injury, which came after he returned from a torn left ACL suffered in 2011, most analysts believe Lattimore would have been the first running back taken in this year’s draft. In just 30 career games at USC, essentially two and a half seasons, he ran for 38 touchdowns, a school record.

“You don’t come across this kind of person very often,” Harbaugh said.

Once Lattimore slipped to the draft’s third and final day, it was almost academic where he would be picked, as long as he was.

A late first-round pick gets about a $7.5 million contract, including a signing bonus around $4 million. When Lattimore went down against Tennessee in October, the possibility of him getting a lucrative first contract vanished.

As the 34th pick of the fourth round, 131st overall, Lattimore will get about what that pick reportedly received last year — a $2.4 million deal, with the only guaranteed money being a $300,584 signing bonus, included in the value of the contract.

While Meeks was one of Saturday’s stunners, because he was not expected to get drafted, Lattimore was probably the day’s most fascinating player. Not because of his draft position or the guaranteed money that his injury cost him, but because of what comes next — the chance to prove he can rebuild his career, just like Gore did.

Gore went from at third-round pick to signing a four-year, $28 million extension in 2007, with about $14 million guaranteed. At February’s NFL combine, Lattimore likened his playing style to Gore’s. Lattimore is 5-11 and 221 pounds, Gore 5-9 and 217 pounds.

“He runs like nobody’s there,” Lattimore said. “He runs with total destruction.”

On Saturday, when one difficult process in Lattimore’s comeback dovetailed into another, it was a comparison he happily embraced again.

“He can catch the ball,” Lattimore said. “I feel like I catch the ball well. He can pass protect. He’s an all-around back. That’s what I’m trying to emulate my style off, because with his success, there’s no question that it works.”