The head coach also provided several other injury updates.
Cornerback Richard Sherman will miss some time with a hamstring strain, which was first reported on Monday morning by Tom Pelissero of NFL Network.
"It will probably be a couple of weeks," Shanahan said of Sherman's status.
Defensive end Dee Ford will also be out a few weeks with a hamstring injury.
"He re-aggravated the same one, so it's going to probably take a little bit longer than it did last time," Shanahan said. "It will probably be at least three weeks."
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Cornerback K'Waun Williams is in the concussion protocol.
As for the injuries leading up to the Week 14 game with the Saints, Shanahan said the team would monitor safety Jaquiski Tartt as he works his way back from a rib fracture.
The 49ers are evaluating treatment options for wide receiver Marquise Goodwin, who is dealing with knee and ankle injuries, which Shanahan called "some chronic stuff."
Shanahan hopes to get wide receiver Dante Pettis (knee sprain) back at practice this week.
Defensive lineman Jullian Taylor (elbow) will likely miss another week.
Next up for San Francisco is a Week 15 matchup at Levi's Stadium against the Atlanta Falcons on Sunday, December 15. That will be followed up by a home game against the Los Angeles Rams, and then the team will finish the season in Seattle against the Seahawks.