49ers’ Twin Tower defense unlikely till season opener

DeForest Buckner (right) and Arik Armstead. DeForest Buckner (right) and Arik Armstead. Photo: Jeff Chiu, Associated Press Photo: Jeff Chiu, Associated Press Image 1 of / 5 Caption Close 49ers’ Twin Tower defense unlikely till season opener 1 / 5 Back to Gallery

Those eager to see the 49ers’ Twin Tower defensive tackles on the field together might have to exercise a bit more patience.

The 49ers’ Arik Armstead and rookie DeForest Buckner, 6-foot-7 first-round picks from Oregon, haven’t played together in the preseason as Armstead has been sidelined with a shoulder injury. Last week, Buckner, the No. 7 pick, was also sidelined with a lower-body, soft-tissue injury in a preseason win against the Broncos.

Head coach Chip Kelly said Buckner has been a full participant in practice this week, a sign he’ll return for Friday’s exhibition game against Green Bay. However, Kelly didn’t sound as optimistic regarding Armstead. He suggested the focus is on making sure Armstead will be available for the regular-season opener against Los Angeles on Sept. 12.

“There’s that fine line that you walk between — he’s got to get reps or if the reps are going to set him back, does he need to get those reps?” Kelly said when asked about Armstead. “The bottom line is that we need to put the best 46 (players) out there when we play (Los Angeles), so we’ll always err on the side of caution from that standpoint.”

Potential debut: Anthony Davis took the majority of first-team snaps at right guard in practice Tuesday, but Kelly didn’t commit to Davis making his NFL debut at the position in Friday’s game.

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“We’ll go through today and tomorrow and a lot of it is feedback from Anthony,” Kelly said. “He’s such a perfectionist. … It doesn’t benefit him or us if he doesn’t feel comfortable there. We’ll continue to work through that.”

Davis, a right tackle in his first five NFL seasons, offered to make the position switch this summer. Davis didn’t play in 2015, and there were questions about his commitment before he returned to the 49ers.

“He’s been fantastic in everything that he’s done since he’s gotten back here,” Kelly said. “The one thing that I truly appreciate about Anthony is that’s a team guy — he’s a team-first guy. ‘Whatever I can do to help this football organization win’ is what he’s all about.”

Receiver injured: Rookie wide receiver Bryce Treggs said he suffered an MCL sprain against Denver and is “week-to-week.” The Cal alum was injured when he caught a 25-yard pass in the second quarter and safety Justin Simmons landed on his knee.

Eric Branch is a San Francisco Chronicle staff writer.