ST. LOUIS (AP) The St. Louis Rams have lost two defensive stalwarts for the rest of the season, with end Robert Quinn to undergo back surgery and hard-hitting safety T.J. McDonald headed for a shoulder procedure.

Coach Jeff Fisher said Wednesday both players will be placed on injured reserve.

St. Louis' pass rush hasn't been the same without Quinn, who has missed three straight games and four of the last five with hip and back injuries. He is second on the team with five sacks.

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''I know his back has been hurting him for quite a bit and he really wanted to wait a long time hoping it would come back,'' middle linebacker James Laurinaitis said. ''He wouldn't have been 100 percent anyway.''

Quinn was second in the NFL with 19 sacks in 2013. He was in double figures in each of the previous three seasons.

''Offenses are going to game plan around his presence,'' Fisher said. ''They're concerned about where he is and what he's doing, and it allows you to a certain extent to dictate a little bit.''

Fisher said the rehab period is 10 to 12 weeks.

''We're being aggressive with this so that he can come back at 100 percent,'' he said. ''Our concern is his future and we need to go ahead and move forward.''

McDonald was sidelined late in Sunday's 27-3 loss to Arizona on a hit from teammate Rodney McLeod. The shoulder had been bothering him for the last few weeks.

''T.J.'s been playing hurt for a while, too,'' Laurinaitis said. ''It's hard to even watch him walk sometimes.''

McDonald is third on the team with 80 sacks and has a sack, a forced fumble and a fumble recovery.

Maurice Alexander, a fourth-round pick last year, is likely to get his first career start at safety Sunday against the Lions.

Quarterback Case Keenum was a full participant for the first time since sustaining a concussion that sidelined him for two games. He'll start Sunday ahead of slumping Nick Foles, benched for the second time this season.

Tight end Lance Kendricks was limited while clearing the concussion protocol, and cornerback Janoris Jenkins, who also sustained a concussion on Sunday, did not practice.

Defensive end William Hayes (thigh) also was held out, and cornerback Trumaine Johnson (thigh) and wide receiver Wes Welker (calf) were limited. Welker was hurt during practice.

Kicker Greg Zuerlein (hip) was a full participant after missing the last two games. Zuerlein said he'll limit his attempts for at least the rest of the year.

''I probably kicked too much after practice, if I could go back, but I don't know if it was just that one thing,'' Zuerlein said. ''This new thing is making sure I keep my ball count down so I'm not hitting however many balls I hit.''

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