SANTA CLARA >> Concern about the 49ers’ offensive line has migrated, from the interior newcomers at last summer’s training camp to the ever-crucial tackle spots for this coming season and beyond.

That’s not to say the 49ers are scrambling like most teams for starting-caliber linemen.

But their right tackle position could be vacated by Mike McGlinchey, if their 2018 top draft pick is not re-signed after five seasons.

Left tackle Trent Williams’ return, at age 35, was no sure thing after his championship quest again was stopped short in the NFC Championship Game. He’ll suit up after back-to-back All-Pro seasons but his long-term forecast is suspect.

With quarterbacks getting hurt left and right, the 49ers obviously want to insulate them with the best protection possible, and that is where free agency could come into play for fortifying their line.

WHO’S HERE >> Tackle: Williams, Colton McKivitz, Jaylon Moore, Leroy Watson, Alfredo Gutierrez.

Guard/Center: Aaron Banks (left), Spencer Burford (right), Jason Poe, Nick Zakelj, Keith Ismael.

Williams is a mesmerizing, athletic wonder who isn’t error-free but is the NFL’s ideal blindside protector. Banks made a steady ascent in his first year starting, and Burford impressed as a rookie while part of an odd platoon with Daniel Brunskill. Center Jake Brendel relished becoming a full-time starting center. Moore seemed to take a step back last season. McKivitz was set to be a restricted free agent, but signed a two-year extension on Thursday and may be the de facto starter at right tackle entering free agency.

PENDING FREE AGENTS >> Tackle: Mike McGlinchey.

Guard/Center: Jake Brendel, Daniel Brunskill.

As great a fit as McGlinchey’s run-blocking is with this scheme, his pass-protection lapses have made him a lightning rod for criticism since his 2018 arrival, even if he admirably started every game last season after major surgery in 2021 on his quadriceps. The 49ers will be in a massive bind at center if Brendel and the versatile Brunskill exit.

EXTERNAL CANDIDATES >> Tackle: Jawaan Taylor (Jaguars), Kaleb McGary (Falcons), Taylor Lewan (Titans), Isaiah Wynn (Patriots), Andrew Wylie (Chiefs).

Guard/Center: Connor McGovern (Jets), Garrett Bradbury (Vikings), Ethan Pocic (Browns), Ben Powers (Ravens), Isaac Seumalo (Eagles), David Edwards (Rams).

The Chiefs’ Orlando Brown will be out of the 49ers’ price range, and Lewan might be more suited for retirement because of knee woes. Some plug-and-play starters are available at center, but Jake Brendel got his shot last year from 49ers offensive line coach Chris Foerster and look for that relationship to continue.