49ers' Jim Harbaugh won't address Alex Boone's holdout

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Jim Harbaugh was asked three questions about contract holdout Alex Boone on Thursday and it was as if he didn't hear them.

The self-described "relentlessly positive" head coach had a theme to push - the opening of training camp was a "rebirth" - and questions about his right guard's dissatisfaction with his contract weren't going to interfere.

At one point, Harbaugh was asked how much Boone's absence detracted from the 49ers' training-camp arrival.

"It's such a positive happening, that first day," Harbaugh responded. "Imagine you're kind of in the comfort of the offseason, like being in the comfort of the womb. You've got plenty to eat in there, it's warm, very cozy. And then you're born into somewhat of the unknown. A lot of people looking at you, a lot of faces looking at you, a lot of excitement. It's light, it's bright, it's noisy, it's the crazy world of football. Again, it's a real happening."

OK, Jim. Follow-up question: Are you disappointed Boone didn't report?

"Again, (I am) relentlessly positive right now," Harbaugh said. "That's how I feel. I'm trying to describe it to you, the rebirth of football. You step out onto that grass of the first practice, smell the smells, see the sky. You've got your team out there. It's a wonderful feeling."

Lattimore sidelined: Now 636 days removed from the gruesome knee injury he sustained at South Carolina, Marcus Lattimore still hasn't fully recovered.

Linebackers hit blocking dummies against the backdrop of the new Levi's Stadium, as the San Francisco 49ers hold training camp to prepare for the 2014 season in Santa Clara, Calif., on Thursday July 24, 2014. Linebackers hit blocking dummies against the backdrop of the new Levi's Stadium, as the San Francisco 49ers hold training camp to prepare for the 2014 season in Santa Clara, Calif., on Thursday July 24, 2014. Photo: Michael Macor, The Chronicle Photo: Michael Macor, The Chronicle Image 1 of / 1 Caption Close 49ers' Jim Harbaugh won't address Alex Boone's holdout 1 / 1 Back to Gallery

The 49ers' running back wasn't on the field Thursday afternoon for the first practice of training camp after he was placed on the non-football injury list last week. Before practice, Harbaugh said Lattimore was placed on the list because of two issues: his surgically reconstructed knee and a hamstring injury he sustained during the offseason program.

"The trainer, doctors evaluate and make those decisions as an organization, and we do what's best for the member of the team, the youngster," Harbaugh said. "Because ultimately that's in our best interest. ... We believe in talking to the (medical staff); we're doing the best thing for Marcus."

Wide receiver Bruce Ellington and center Marcus Martin, two rookie draft picks, also are on the non-football injury list. They sustained ankle injuries away from the facility in the month between the end of the mandatory minicamp and the start of training camp. Harbaugh said both would join practice soon with Ellington, who was a point guard at South Carolina, being the first to come off the injury list.

"It doesn't seem to be anything real serious," Harbaugh said. "Both involved rolling an ankle. Basketball-type rolling of the ankle. Not playing basketball, according to them. And you have to take a man at his word. Said they were doing football drills."

Tight end Garrett Celek was placed on the Physically Unable to Perform list Wednesday. Harbaugh said Celek's back stiffened after he passed the team's conditioning test. He will have an MRI exam.

Defensive tackle Justin Smith and right tackle Anthony Davis, who both had offseason shoulder surgeries, were the only players on the active roster who didn't practice Thursday.