After having an MRI earlier this week, the 49ers determined defensive lineman Quinton Dial is expected to be available for the season opener Sept. 12 against the Rams, coach Chip Kelly said Tuesday.

Dial came down with a left knee injury in the first half of San Francisco’s third preseason game against the Packers and has not practiced since. He’s been in street clothes with a heavy brace on his left knee.

Dial’s prognosis is good news for San Francisco, who will rely heavily on the former fifth-round pick once the regular season begins. He signed a three-year contract extension after becoming a full-time starter for the first time in 2015.

In the absence of Ian Williams and Glenn Dorsey, who appears close to returning to action after tearing an ACL in November, Dial is the 49ers’ best run defender along the defensive line.

Former 2015 first-round pick Arik Armstead hasn’t played in the preseason while dealing with a left shoulder injury, but is expected to be ready for the start of the season. This year’s first-round pick DeForest Buckner missed the second preseason game with a lower-leg, soft tissue injury, general manager Trent Baalke told reporters.

Kelly said Dial will be held out of the team’s preseason finale Thursday in San Diego, as expected.