A fifth-year pro, Brown missed the final nine games of the 2007 season with a right knee injury.
The Dolphins had hoped that Brown might be able to return this season, but they made the roster move after he was examined by a specialist. It's a big blow for a team that ranks fourth in the NFL in rushing and 30th in passing.
A league source told NFL Network's Jason La Canfora that Brown will see a specialist Thursday morning to further evaluate the specifics of his foot problem. He may or may not need surgery at this point, pending the results.
The move was announced shortly after the Dolphins (4-5) departed for Thursday night's game against the Carolina Panthers. Ricky Williams, the 2002 NFL rushing champion, will replace Brown in the Dolphins' starting lineup.
Brown was on pace for the best year of his career with 648 rushing yards and eight touchdowns, and he also threw for another score. He was the triggerman in Miami's Wildcat offense, and it's uncertain how much the Dolphins will use the package with Williams taking snaps.
Williams has rushed for 558 yards. He's coming off his first 100-yard game of the season and is averaging a career-best 5.3 yards per carry, but he's 32, and it's uncertain whether he can handle a workhorse role.
The Dolphins' backup running back now is 2008 sixth-round draft pick Lex Hilliard, who has yet to carry the ball in an NFL regular-season game. Reserve running back Patrick Cobbs was sidelined for the season by a knee injury last month.
For Brown, the setback could be costly, because he's in the final year of his rookie contract. Depending on when a collective bargaining agreement is reached, he could become a free agent after this season, and a second major injury in three seasons is sure to hurt his market value.
Brown rebounded from his 2007 knee injury to start 13 games last season. He rushed for 916 yards and 10 touchdowns to earn his first Pro Bowl selection.
The Associated Press contributed to this report.