MIAMI (AP) -- Ronnie Brown's season has ended with an injury -- again.

The Miami Dolphins' leading rusher was placed on injured reserve Wednesday because of a right foot injury suffered in Sunday's victory over Tampa Bay.

A fifth-year pro, Brown missed the final nine games of the 2007 season with a right knee injury.

The Dolphins had hoped Brown might be able to return this year but 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.

The move was announced shortly after the Dolphins (4-5) departed for Thursday's game against Carolina. Ricky Williams, the 2002 NFL rushing champion, will replace Brown in the starting lineup.

Brown was on pace for the best year of his career with 648 yards rushing and eight touchdowns, and he threw for another. He was the triggerman in the wildcat, 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 backup running back is now 2008 sixth-round draft pick Lex Hilliard, who has yet to carry the ball in the NFL. 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 knee injury to start 13 games last season to rush for 916 yards and 10 scores.

To replace him on the roster, the Dolphins signed safety Nate Ness from the practice squad.