SANTA CLARA -- Quarterback Jimmy Garoppolo took part in some throwing on Tuesday and is scheduled for limited practice on Wednesday, 49ers coach Kyle Shanahan said.
Rookie quarterback Trey Lance is likely to take most of the first-team practice snaps, Shanahan said, with Garoppolo taking as much practice time as he can handle comfortably with his thumb injury.
"It won't be a full-speed practice, so it won't be as challenging," Shanahan said Wednesday on a video call with Bay Area reporters.
Shanahan said if Garoppolo is near 100 percent he would start Sunday against the Los Angeles Rams in a game that could determine whether the 49ers make the playoffs.
Shanahan said he does not know at this stage in the week who will be the 49ers' starter on Sunday. He said he will not make an announcement on the starter before kickoff due to competitive reasons.
Garoppolo sustained a grade-3 tear of the ulnar collateral ligament in his right thumb on Dec. 23 against the Tennessee Titans. He did not practice at all last week and was inactive for the 49ers' game Sunday against the Houston Texans.
The 49ers (9-7) enter the Week 18 game in control of their own destiny for a playoff spot. If the 49ers beat the Rams, they will make the playoffs as the No. 6 seed. The 49ers would also make the playoffs if the New Orleans Saints lose to the Atlanta Falcons.
Lance made his second NFL start on Sunday, and threw for 249 yards and two touchdowns in the 49ers' 23-7 victory over the Texans.
On the season, Lance has completed 41 of 71 pass attempts (57.7 percent) for 603 yards with five touchdowns and two interceptions and a passer rating of 97.3.