Leftwich started the first six games, completing 59% of his passes for 1,159 yards, with seven touchdowns and five interceptions.
He said he initially hurt his left ankle Oct. 1 at Washington, and the injury flared up nearly two weeks later. Leftwich convinced coaches he could play at Houston, then performed poorly in a loss to the Texans.
He was benched the next week in favor of David Garrard, who has led the Jaguars to a 3-2 record since replacing Leftwich.
Leftwich underwent surgery Nov. 21 to clean up the area around the ankle and hoped to return this season. But the Jaguars put him on injured reserve and signed defensive back David Richardson from the practice squad.
Richardson could provide depth and special teams help Sunday at Miami. Safety Nick Sorensen (hamstring) and running back Montell Owens (shoulder), two of the team's top special teams players, were downgraded to doubtful on the injury report.
Richardson, a third-year player from Cal Poly San Luis Obispo, has four tackles in nine games over three seasons with the Jaguars.
The Indianapolis Colts figure to get a big boost on Sunday against the Tennessee Titans with the expected returns of receiver Brandon Stokley, safety Bob Sanders and outside linebacker Gilbert Gardner.
Sanders has not played in eight of the Colts' last nine games because of soreness and swelling in his right knee. He had arthroscopic surgery on the knee in September.
Stokley had been sidelined since Oct. 8, when he sprained his left knee during the fourth quarter of the Colts' home game against the Titans. Gardner (ribs), who sat out last week's game against the Philadelphia Eagles, is listed as questionable.
Diem (back/abdomen) and Bethea (shoulder) have not practiced this week. Clark is out indefinitely after straining a ligament in his right knee. The Colts have not yet ruled him out for the season.
Campbell and safety Troy Vincent were the only players not to take part in a full practice Friday. Vincent, who sat out last week's game because of a sore hamstring, is listed as questionable. Right tackle Jon Jansen practiced and was expected to play, despite a nagging calf injury that had him limping noticeably this week.
Cleveland Browns starting right tackle Ryan Tucker is battling an undisclosed mental disorder and will not play the rest of the season, the team said.
The Browns refused to disclose more details about Tucker's illness, saying only that it was a common disorder not related to football. The 10-year veteran hopes to return to football next season.
Thomas, the Jets' first-round pick out of Alabama Birmingham in 2002, has a career-high five sacks, including two last Sunday against Houston, and is sixth on the team with 58 tackles.
Running back Willis McGahee of the Buffalo Bills did not practice because of an illness, but he should be ready to play Sunday against the San Diego Chargers, Coach Dick Jauron said.
McGahee rushed for 63 yards and two touchdowns in the Bills' 27-24 win over Jacksonville last week. He sat out the previous two games after breaking three ribs against Green Bay on Nov. 5.