Derek Anderson’s season is officially over, yet another slap for the down-on-their-luck Cleveland Browns.

Anderson, who lost his starting job to Brady Quinn several weeks ago, will miss the final four games after tearing a ligament in his left knee on Sunday against Indianapolis.

An MRI taken Monday revealed Anderson tore the medial collateral ligament when he was sacked in the final minutes of Cleveland’s 10-6 loss to the Colts. Anderson, making his first start since Nov. 2 after being benched for Quinn, will not need surgery. He will be placed in a brace and will need four to six weeks to recover.

Quinn, too, is done for the season with a finger injury. He has not yet decided whether to have surgery on his broken right index finger, which he hurt on Nov. 17 at Buffalo.

The injuries to their top two QBs means the Browns (4-8) will start third-stringer Ken Dorsey on Sunday against the Tennessee Titans (11-1). Return specialist Joshua Cribbs, who played quarterback at Kent State, will serve as Dorsey’s backup unless the Browns can sign a veteran quarterback in the next few days.

‘‘Once Derek came back in we were all confident because we know Derek can play and its frustrating now that we have to change again,’’ guard Eric Steinbach said.

Coach Romeo Crennel said the club will try to find another quarterback familiar with Cleveland’s system.

Dorsey went 2-8 as a starter for the San Francisco 49ers in 2004-05. In college, he was 38-2 as a starter at Miami and won a national championship in 2001. Dorsey hasn’t completed a pass in an NFL game in three years, and has attempted just four since joining the Browns in 2006.

Dorsey’s previous start also came against the Titans in 2005. Then with San Francisco, he completed 23 of a career-high 43 passes for 192 yards with one touchdown and an interception.

‘‘He’s a very smart quarterback and he’s a competitor,’’ Crennel said. ‘‘He probably doesn’t have some of the physical skills that some other quarterbacks in the NFL have. I think that’s probably been the biggest drawback.’’

Unfortunately, Dorsey won’t have won of his favorite targets as tight end Kellen Winslow will also sit out this week after sustaining a high ankle sprain on Sunday.

Winslow, who played in college with Dorsey, will be fitted with a walking boot for one week, but it’s still too early to determine if he’ll play again this season.

Dorsey will try to keep things simple.

‘‘I just try to go out and do what I’m supposed to do,’’ he said. ‘‘I try to get the ball to guys who run fast and I try to make good decisions out there.’’

If Anderson’s injury wasn’t tough enough to take, some Browns fans made it worse by cheering when the former Pro Bowler crumpled to the turf.

The negative reaction was not well received by Anderson’s teammates.

‘‘It made me upset,’’ defensive tackle Shaun Smith said. ‘‘When you see stuff like that happening, it could have been a career-ending injury. He was your quarterback last year and went to the Pro Bowl, everybody was cheering for him then. For you to cheer for him to get hurt, that’s not good, that’s like me being at your family member’s funeral and being happy they died. That’s not a good sign.

‘‘For people to cheer, that’s no class at all.’’

Along with not living up to high expectations, the Browns are enduring a season to forget.

They’ve had a high number of injuries along with some controversy (Winslow’s staph infection, Anderson’s benching) and turmoil (GM Phil Savage’s profane e-mail to a fan). Crennel, who broke into the NFL as an assistant in 1981, was asked to rank this season among his nearly 30 in the league.

‘‘This has been pretty tough,’’ he said. ‘‘But you just work through it, that’s what you do.’’

Crennel has seen better days.

So have the Browns, whose 2008 season is in ruins.

They’ve lost four straight home games and will likely hit double-digit losses for the fourth time in six years. Times have become so desperate in Cleveland that a vocal segment of their die-hard fans is touting Bill Cowher, the former chisel-chinned coach of the hated Pittsburgh Steelers, as their savior.

On Sunday, fans in the notorious ‘‘Dawg Pound’’ bleachers held up signs that said ‘‘Cowher Power.’’

While rumors swirl, Crennel remains steadfast. He is unwavering, committed. Hired by Cleveland in 2005 after winning his fifth Super Bowl ring as an assistant, the man affectionately known by his initials as ‘‘RAC’’ is staying above the fray. He hasn’t quit, and neither have his players as evidenced by their 10-6 loss to the Colts.

‘‘They played really hard,’’ Crennel said. ‘‘I think they respect me.’’

It goes deeper than that with some of the Browns, who find it unfair that Crennel has been singled out and may be the one to pay for their multitude of sins.

‘‘We’re all behind RAC 100 percent,’’ said linebacker Willie McGinest, who also played under Crennel in New England. ‘‘He’s one of the few men in here, one of the people in here who cares about us, who gives us every opportunity to win, who works as hard we do, takes our losses as hard as we do and tries to do everything he can.’’

Owner Randy Lerner said last week that he’ll wait until after the season before evaluating Crennel and Savage. Crennel, who received an extension through 2011 after leading the Browns to 10 wins in 2007, is 24-36 without a playoff appearance in his four seasons.

‘‘People don’t care about whether it’s fair or not, they care about whether you win or lose,’’ Crennel said. ‘‘That’s the nature of this business. I didn’t have any rose-colored glasses on when I took the job. I’ve been in this league for 30 years and I’ve seen a lot of things happen in 30 years. And most of it has to do with winning and losing.’’