Brown, a senior who has rushed for 413 yards this year, broke his collarbone in a 35-14 loss to the Volunteers on Saturday and will miss four-to-six weeks, head coach Mark Richt said Sunday.
"It's a shame," Richt said. "He's probably the toughest guy on our football team. I know he would play with it. He's just that tough, but we can't take that risk."
Richt initially said Brown would be out six weeks and then amended his statement to four-to-six. If Brown misses six weeks, he would be back for the regular season finale Nov. 24 against Georgia Tech. If he missed any more time, his only remaining game as a Bulldog would be a bowl game.
Brown missed the final six games of 2006 due to a torn ACL, which he rehabbed in time to earn the starting tailback spot for the first game of the year.
"If he heals bones like he rehabs ACLs, who knows?" Richt said.
Along with starting at tailback, Brown is Georgia's kickoff return man, a gunner on the punt coverage team and a safety on the kickoff coverage team.
"We need more guys that would play like Thomas," Richt said.
Senior tailback Kregg Lumpkin or redshirt freshman Knowshon Moreno will take Brown's place as the starter, Richt said. Lumpkin, who still is bothered by a broken thumb suffered in the third game of the season, rushed four times for 26 yards against the Volunteers. Regardless of who starts, Lumpkin and Moreno will divide the carries much the same as Brown and Moreno did, Richt said.
Georgia fell 12 spots after its loss to the Volunteers and barely stayed in the national rankings at No. 24, one spot ahead of Tennessee.
The Bulldogs (4-2, 2-2 SEC) play Vanderbilt on Saturday at 6 p.m. in Nashville, Tenn. The game will be televised by ESPN2.
It has been almost 50 years since the Commodores (3-2, 1-2) beat Georgia in back-to-back games, but it could happen this year. Vanderbilt won 24-22 in Athens last year.
"We're definitely going to have that in the back of our heads," senior center Fernando Velasco said.
What should be on the forefront of every Bulldogs mind is holding onto his starting job. Richt floated the idea of depth chart changes immediately after the game and confirmed it Sunday, but he declined to offer specifics.
"There will be a few change here and there," he said. "We're not exactly sure (where) yet."