San Francisco 49ers All-Pro left tackle Trent Williams has visited with specialists about his lingering ankle injury that will end up sidelining him for the final seven games of the regular season.

Williams, 36, has dealt with ankle issues throughout his 14-season career, and head coach Kyle Shanahan has said his latest injury has healed slower than expected. Shanahan was asked Thursday whether Williams’ injury could be career-threatening.

“Not that we’ve heard of,” Shanahan said. “There’s always concern that it’s taken longer to heal than expected, but he’s seen a number of specialists. Plus, he’s seen our own (doctors). Everyone is pretty much on the same page. He just needs some time and it will heal. So there’s really no worries there. We just wanted it to heal faster.”

Shanahan has said Williams took a Toradol shot to play with his injury in a 20-17 loss to the Seahawks on Nov. 17. Williams hasn’t played since and it appeared he had a knee scooter by his chair on Dec. 12 when he was shown watching the 49ers’ 12-6 loss to the Rams from a suite at Levi’s Stadium.

The 49ers officially placed Williams on injured reserve Thursday and the 49ers signed offensive tackle Matt Hennessy off the Falcons’ practice squad. Hennessy, 27, a 2020 third-round pick of Atlanta, has made 22 starts in his 45-game career.

Greenlaw shelved: Linebacker Dre Greenlaw won’t play in the final two regular-season games due to a right calf injury that limited him to four snaps in Sunday’s loss to the Dolphins.

Greenlaw was playing in his second game after tearing his left Achilles in Super Bowl LVIII in February. He was forced to leave a 12-6 loss to the Rams on Dec. 12 early in the third quarter with left knee and Achilles soreness before exiting after the first series against Miami.

“Obviously, we’d like to have had him to finish the season off, especially myself,” linebacker Fred Warner said. “At the end of the day, his health is what’s most important.”

As for Warner, who has played the past 11 games with a broken bone in his right ankle, he said he has given no thought to sitting out the final two games.

“I think there’s an integrity to the game,” Warner said. “There’s an integrity to your team. If you are willing and able, you need to be out there with that 49er red on you, regardless of the situation.”

Injury report: The 49ers could be forced to start their fourth-string left tackle, whoever that is.

Shanahan said Spencer Burford could miss Monday’s game against the Lions due to a calf injury he suffered against the Dolphins. Burford, a guard, was injured while replacing second-string left tackle Jaylon Moore, who has been placed on injured reserve with a quadriceps injury.

To address the shortage at the position, the 49ers signed Hennessy and they also signed Charlie Heck off the Cardinals’ practice squad Wednesday. Heck, a 2020 fourth-round pick, has made 21 career starts. Last week the 49ers signed offensive tackle Austen Pleasants, 27, who has played 10 offensive snaps in three career games.

With Burford sidelined in Thursday’s practice, Shanahan was asked whether Heck would receive first-string snaps at left tackle.

“We’re going to work him at a couple spots, see what he can do for us,” Shanahan said. “We’ve got to mix and match a number of guys.”

In other injury news, Shanahan said left guard Aaron Banks, a pending free agent, should be recovered in several weeks after suffering a season-ending MCL injury Sunday. Running back Isaac Guerendo (foot, hamstring), safety Ji’Ayir Brown (ankle) and defensive end Robert Beal (ankle) were limited in practice.