KNOXVILLE, Tenn. (AP) -- Tennessee quarterback Justin Worley is out indefinitely after undergoing surgery on his right thumb.
Volunteers coach Butch Jones announced the severity of Worley's injury after Tuesday's practice and said he believes Worley has a torn ligament. Knoxville radio station WNML had reported earlier Tuesday that Worley would miss about four weeks.
''He'll be out an indefinite period of time,'' Jones said. ''Everything is how the body heals. It could be two weeks. It could be three weeks. It could be four weeks. We'll see how he progresses.''
Worley's injury means freshman Joshua Dobbs will make his first career start Saturday when Tennessee (4-4, 1-3 SEC) plays at No. 10 Missouri (7-1, 3-1). Dobbs replaced an injured Worley in the second half of a 45-10 loss to No. 1 Alabama last week.
Freshman Riley Ferguson is listed as the second-team quarterback. Redshirt freshman Nathan Peterman practiced Tuesday, but his status for the Missouri game remains uncertain. Peterman has missed four games since undergoing surgery on his right hand after a 31-17 loss at Florida on Sept. 19.
''I'm comfortable with both (Dobbs and Ferguson),'' Jones said. ''They both have done a great job, but I think we're going to lean toward the game experience that Josh was able to garner in the Alabama game.''
Worley appeared to have his thumb or hand examined on the sideline Sept. 28 in a 23-21 victory over No. 14 South Carolina, though he never left the game. Worley got hurt more seriously against Alabama. Jones said he thought Worley aggravated the injury while making a tackle after throwing an interception in the Alabama game.
''He slightly injured it a little bit (against) South Carolina, but he practiced all week and he felt it on the one tackle in the Alabama game,'' Jones said. ''It's hard to tell really when it happened, but it happened. The surgery was successful, and we look forward to getting him back.''
Worley has completed 55.6 percent of his passes for 1,239 yards with 10 touchdowns and eight interceptions. Dobbs replaced Worley in the second half against Alabama and went 5 of 12 for 75 yards. Dobbs also rushed for 19 yards on three carries.
Tennessee scored all 10 of its points against Alabama after Dobbs entered the game.
Dobbs will become the third Tennessee quarterback to start a game this season. Worley started seven of the Vols' first eight games. Peterman started against Florida.
The Vols are hoping Dobbs' stellar academic background shows he can be a quick study on the field. Dobbs won the Watkins Award given annually by the National Alliance of African-American Athletes to a high school senior who combines academic and athletic excellence.
''We've got confidence in him,'' sophomore wide receiver Alton ''Pig'' Howard said. ''We've always had confidence in him.''
NOTES: Jones said the NCAA has informed Tennessee that its football program should ''have no APR (Academic Progress Rate) issues moving forward'' after improving its performance in that particular statistic, used by the NCAA to measure academic progress. APR figures released last summer showed Tennessee had the lowest score over the past four years of any SEC football program and faced potential penalties if it hadn't improved. ... Jones expects safety Brian Randolph to play against Missouri. Randolph and safety Byron Moore both practiced Tuesday while wearing green non-contact jerseys.