Matt Cassel will start at quarterback in the Vikings' season finale against the Lions on Sunday, with Christian Ponder as the backup. Josh Freeman is expected to be inactive for the ninth time in 12 games since joining the Vikings.

"I don't know what would change that as the week goes on, but that's the thought process as we speak," coach Leslie Frazier said Monday.

Cassel had his worst game this season in Sunday's 42-14 loss at Cincinnati. He was 13 of 27 for 114 yards with a touchdown, three interceptions and a fumble. Frazier will stick with Cassel, who has the option to become an unrestricted free agent during the offseason.

Cassel can opt out of his contract at season's end, and Ponder is signed through 2014. Freeman, who signed during the season, will become an unrestricted free agent. He started one game, two weeks into his tenure, against the Giants and posted the team's lowest team quarterback rating this season (40.6) before Cassel's performance on Sunday (32.6)

"[Freeman] picked up things well and worked hard in practice," Frazier said. "He's still doing those things, picking up the offense, working hard, spending time with coaches doing all the things he needs to do. But with one game left and having a chance to watch Matt play again, we made the decision and that's probably the way we'll go."

Injury update

Frazier doesn't expect to have middle linebacker Audie Cole against the Lions, but he's holding out hope on running back Toby Gerhart and cornerback Xavier Rhodes.

Matt Cassel, not Christian Ponder or Josh Freeman, is ticketed to start the final game at the Metrodome for the Vikings.

Cole suffered a high ankle sprain in Sunday's loss and wore a walking boot after the game. He had just five snaps on defense before the injury.

Erin Henderson replaced Cole at middle linebacker and recorded a game-high 12 tackles.

"[Henderson] came in, made some nice tackles for us, did a pretty good job of directing defense," Frazier said. "I thought he did a pretty good job of moving over from the outside linebacker spot to the middle linebacker spot."

Gerhart aggravated a hamstring injury after only two snaps.

Rhodes hasn't practiced in two weeks since injuring his ankle against the Ravens. He did some light conditioning twice last week, but never was cleared by the training staff to participate.

"We definitely need him, so we'll see if he's able to practice tomorrow or when we come back after practice," Frazier said. "But we're hoping so."

Tight end John Carlson was placed on injured reserve because of a concussion on Saturday. He was cleared by the training staff during the week but felt symptoms after one practice.

Carlson has a long history with concussion symptoms and told the Star Tribune last week he could consider retiring at the end of the season.

Not in a rush

The Vikings pass rush has struggled this season, and opposing quarterbacks have frequently taken advantage. The Vikings are last in the league in pass defense, giving up 294.4 yards per game.

"We haven't been as consistent rushing the passer as we have been in the past and that definitely affects what we try to do systematically," Frazier said. "A lot of what we do revolves around being able to rush with four, and we haven't had that consistent rush like we've had in the past."