San Francisco 49ers quarterback Jimmy Garoppolo plays against the Tennessee Titans in the first half of an NFL football game Thursday, Dec. 23, 2021, in Nashville, Tenn. (AP Photo/Wade Payne)

49ers QB Jimmy Garoppolo suffered a right thumb injury in Thursday’s loss. ESPN reported a torn ligament and fracture.

Quarterback Jimmy Garoppolo suffered an injury to his right thumb in Thursday’s loss to the Titans that has clouded his status for the rest of the 49ers’ season.

Though the team characterized the injury as a sprain, ESPN reported Garoppolo suffered a torn ulnar collateral ligament (located in the lower thumb) and a fracture. Dr. Nirav Pandya, the associate professor of UCSF orthopedic surgery, said that surgery to repair such an injury involves a recovery timeline of four to six weeks.

Pandya was skeptical Garoppolo could play effectively through the injury if a brace was used to support his thumb. The UCL is key for stability and grip strength.

“The tough thing with this injury is it makes it really hard to grip the ball,” Pandya said. “That’s where the issue of him trying to play comes in. … With a lineman or non-skill-position player, you could try taping it and bracing it and just getting (surgery) done at the end of the season.

“But for a quarterback, that is really hard. It doesn’t really matter how much you can gut it out. The problem is that the thumb is unstable.”

Rookie Trey Lance, the third overall pick of the 2021 NFL draft, will make his second career start if Garoppolo is unable to play against Houston on Sunday at Levi’s Stadium. Lance hasn’t thrown a pass in a game since he started in a 17-10 loss at Arizona on Oct. 10, when Garoppolo was sidelined with a strained calf.

The 49ers (8-7), currently the No. 6 seed in the NFC playoff chase, could need to beat Houston and the Rams in their regular-season finale to secure a postseason berth.

Garoppolo did play through the injury in the 20-17 loss at Tennessee after he was hurt when he was sacked by defensive end Denico Autry with about four minutes left in the second quarter.

Garoppolo was able to function without a notable dropoff in his performance. Garoppolo completed 13 of 16 passes for 136 yards with one interception before he was injured. He completed 13 of 19 passes for 186 yards with a touchdown and a pick after his injury.

Head coach Kyle Shanahan characterized Garoppolo’s injury as a “sprain” on Monday during a conference call. Later, however, ESPN reported his injury was “more significant” than a sprain before adding that Garoppolo had a broken thumb and torn ligament.

Despite Garoppolo’s ability to play through his injury against the Titans, Shanahan indicated the thumb’s functionality had decreased four days after the game. Garoppolo was not observed by reporters during the portion of practice open to the media Monday.

“It didn’t feel great today,” Shanahan said. “He wasn’t able to throw today. And we’ll see how it is on Wednesday. Hopefully, it will get better.”

Shanahan said Garoppolo’s injury had an impact on his second interception, which came on his first pass of the third quarter. Garoppolo targeted wide receiver Deebo Samuel on a crossing route, but his pass sailed high and was corralled by safety Amani Hooker.

“I would say that was the one play it affected him the most,” Shanahan said.

Garoppolo ranks second in the NFL in yards per pass attempt (8.5), seventh in completion percentage (68.0) and eighth in passer rating (99.6). He is among six QBs who rank among the league’s top 10 in those categories. The others are Green Bay’s Aaron Rodgers, Cincinnati’s Joe Burrow, Arizona’s Kyler Murray, Dallas’ Dak Prescott and the Chargers’ Justin Herbert.

Lance, 21, has appeared in just one game since his start Oct. 10, playing five mop-up snaps in a 30-10 win at Jacksonville on Nov. 21. He has completed 25 of 48 passes for 354 yards with three touchdowns and one interception this season. He also has rushed for 137 yards on 30 carries with a touchdown.

Shanahan said Lance’s accuracy and decision-making have improved over the past month while he has served as the scout-team QB in practice.

“I think this last month for Trey had been his best consecutive four weeks of practice since we’ve had him,” Shanahan said. “He’s had a number of good days and he’s had some bad days, like most guys do. As far as his consistency, I feel like this last month has been his best.”

Lance was sidelined for three weeks after he suffered a knee injury in his start against the Cardinals. He also suffered a broken right index finger in the preseason finale against the Raiders on Aug. 29. Shanahan indicated that injury impacted Lance’s accuracy early in the season.

“I think anytime you have a broken bone in your finger, it’s always going to affect how you throw,” Shanahan said. “That doesn’t mean you can’t do it. It definitely is a challenge. I think as the year has gone and it’s healed up more, I think it’s helped him.”

Asked if Garoppolo’s season is likely over, barring an unforeseen development, Pandya paints a picture in which fans should expect Lance will be the 49ers’ starting QB on Sunday and beyond.

“That would be my guess based on what’s being reported,” Pandya said. “I think it would be very hard for a quarterback to either play at all, or play effectively, with this injury. That would be my educated guess.”

Eric Branch covers the 49ers for The San Francisco Chronicle. Email: ebranch@sfchronicle.com Twitter: @Eric_Branch

Eric Branch has worked at the San Francisco Chronicle since 2011 as the 49ers beat writer. Before that, he covered the 49ers for the Santa Rosa Press Democrat in 2010. Since he began his career in journalism in 1997 in Logansport, Ind., he's covered events ranging from archery tournaments to the NCAA Men's Basketball Tournament.