SANTA CLARA — San Francisco coach Kyle Shanahan said the team is getting close to ruling out star left tackle Trent Williams for the rest of the season as his injured ankle isn’t healing as fast as the 49ers hoped.

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Williams has missed the past four games with the injury as the Niners (6-8) have fallen to the brink of playoff elimination and he is unable to get back to practice at the start of this week.

That raised questions about whether San Francisco would be better off shutting the 36-year-old Williams down and start getting him ready for next season.

“If he can get back to healthy we would play him,” Shanahan said Wednesday. “But it’s not like that right now. So it’s getting closer to being that way.”

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Injuries Mount for 49ers

The 49ers also were missing running back Isaac Guerendo at practice Wednesday as they prepare to face Miami. Guerendo hurt his hamstring in a loss last Thursday night against the Los Angeles Rams. Guerendo has taken over the starting role with both Christian McCaffrey and Jordan Mason out with injuries.

Linebacker Dre Greenlaw was limited at practice after coming out of his first game since tearing his left Achilles tendon in the Super Bowl with soreness in his knee.

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Campbell Suspension Fallout

Greenlaw’s return led to the benching of De’Vondre Campbell, who refused to play in the game Thursday night. That led the 49ers to suspend Campbell for the final three games for conduct detrimental to the team.

Shanahan said the team looked into Campbell’s history before signing him as he had made public complaints about his usage in Green Bay. But ultimately the team decided Campbell was the best option after Eric Kendricks chose to sign with Dallas instead of the 49ers and another player the team targeted also signed somewhere else.

“We obviously made a mistake,” Shanahan said. “It’s not something you don’t look into. You look at everything and you weigh the risk and reward or stuff and you weigh the situations that you have and what decisions you can make in terms of options. By no means was it our first option. But at the time when it went down we thought it was our best option and it didn’t work out.”

Campbell’s play was spotty during his time with San Francisco and the return of Greenlaw last week showed what the defense had been missing.

Greenlaw made eight tackles in the first half and brought a physical element to the run defense that had been lacking at times this season.

“The way that he moved on (Thursday), you would never have known that he went through that,” teammate Fred Warner said. This guy’s unbelievable.”

Injury Updates

NOTES: DE Nick Bosa (oblique), S Malik Mustapha (chest, shoulder), OL Jaylon Moore (hip) and OL Nick Zakelj (illness) were all expected to be limited in practice.