Niners' backup center has kneecap injury

Recommended Video:

Niners rookie center Marcus Martin is expected to be sidelined about eight weeks after he suffered a kneecap injury in Sunday's 21-7 win over San Diego, a source told The Chronicle.

Martin, 20, a third-round pick, is the second-string center behind Daniel Kilgore and is also capable of playing guard. Head coach Jim Harbaugh mentioned Adam Snyder and Joe Looney as the top candidates to assume Martin's backup duties at center.

Snyder, 32, started three games at center for the Cardinals in 2012. Looney, who is the starter at right guard with Alex Boone in the midst of a contract holdout, has had practice time at center since he was drafted in the fourth round in 2012.

The 49ers have three options with Martin: They can place him on injured reserve, put him on injured reserve with the designation to return or carry him on the 53-man roster.

Still smiling: Mike Iupati's humor remained intact a day after he was torn up by Corey Liuget.

Quarterback McLeod Bethel-Thompson was among the roster cuts. Quarterback McLeod Bethel-Thompson was among the roster cuts. Photo: Carlos Avila Gonzalez, The Chronicle Buy photo Photo: Carlos Avila Gonzalez, The Chronicle Image 1 of / 1 Caption Close Niners' backup center has kneecap injury 1 / 1 Back to Gallery

On the heels of a forgettable performance against the Chargers, the 49ers' left guard was queried by a late-arriving reporter who had a question Iupati had probably fielded.

"Sorry," the reporter said. "I got here a little late. I'm sure you want another question about" Sunday.

"Oh," Iupati said, with a weak smile as he looked to another reporter, "can you give him your notes?"

To his credit, Iupati fielded every question after he allowed a sack to Liuget that led to a lost fumble by Colin Kaepernick and allowed another pressure by the Chargers' defensive end. San Diego linebacker Dwight Freeney also shed Iupati's block to drop running back LaMichael James for a 2-yard loss.

Iupati is a two-time Pro Bowler, thanks mainly to his run-blocking ability. Last year, he ranked 49th out of 59 guards in Pro Football Focus' pass-blocking efficiency ratings.

"You just watch film and sometimes you win some and you lose some," Iupati said. "It's mainly technique."

Roster moves: The 49ers placed running back Marcus Lattimore on the reserve non-football injury list, meaning the 2013 fourth-round pick will be sidelined for at least the first six games of the season.

The move came as they cut their roster to 75 in advance of Tuesday's 1 p.m. deadline.

The 49ers also placed LB NaVorro Bowman (knee) on the reserve/physically unable to perform list, sidelining him for at least six games. TE Garrett Celek (back) and DT Kaleb Ramsey (undisclosed) also went on the PUP list.

The 49ers placed three 2014 draft picks - FB Trey Millard, CB Keith Reaser and G Brandon Thomas - on the non-football injury list.

The 49ers released WR David Reed and waived QB McLeod Bethel-Thompson, S D.J. Campbell, TE Kevin Greene, RB Jewel Hampton, P Colton Schmidt, LB Kion Wilson and WR Devon Wylie. The 49ers released LB Blake Costanzo from injured reserve.