The wide receiver was one of four Philadelphia Eagles to tear an ACL in training camp. The Eagles really felt Maclin's absence in last week's loss to Kansas City. Jackson was held to just three catches after having 16 receptions for 297 yards and two touchdowns in the first two games.
"We never look at it if we had Jeremy Maclin, it's a different situation," Kelly said Tuesday. "I don't think it's productive to think about it that way. It's not going to change. Mac isn't coming back until next year."
Several NFL teams face similar problems. Replacing important starters with capable backups often can be the difference between missing the playoffs and playing in January. It's not always the best teams that win in the end, but the healthiest ones with the most depth.
ACL injuries are perhaps the most significant because they're season-ending and require a longer recovery time, but plenty of other body parts besides the knee are knocking players out of the lineup.
Here are five common injuries putting players on the sideline:
ACL/KNEE: A torn anterior cruciate ligament used to be a devastating injury. Modern medicine changed that, and many players come back and perform at a high level. Check Adrian Peterson. Still, it's a big deal because guys are out for the year.
Packers left tackle Bryan Bulaga, Chargers wide receiver Danario Alexander, Giants free safety Stevie Brown, Broncos center Dan Koppen, Colts defensive tackle Brandon McKinney and Dolphins tight end Dustin Keller were among those who tore ACLs in the summer.
Since the season opener, Steelers center Maurkice Pouncey and running back LaRod Stephens-Howling, Colts running back Vick Ballard, Panthers guard Garry Williams and Bears defensive tackle Henry Melton joined the list.
Ravens wide receiver Jacoby Jones, Lions running back Reggie Bush and Cowboys defensive end Anthony Spencer also have been sidelined by other knee injuries this season.
CONCUSSION: Raiders quarterback Terrell Pryor had his best passing day before leaving Monday night's loss to Denver with a concussion. It's uncertain when Pryor will return, but his concussion isn't as severe as the one that ended the season for Bills quarterback Kevin Kolb.
Texans wide receiver Andre Johnson, Packers tight end Jermichael Finley and running back Eddie Lacy, Eagles cornerback Bradley Fletcher, Redskins safety Brandon Meriweather, Panthers cornerback Josh Thomas, Bengals defensive end Michael Johnson, Giants cornerback Prince Amukamara, Chargers right tackle D.J. Fluker and 49ers safety Eric Reid are among those who've suffered concussions so far.
HAMSTRING: Clay Matthews became the latest Packers player to injure a hamstring during a 34-30 loss to Cincinnati on Sunday. He joins safety Morgan Burnett, cornerback Casey Hayward and fullback John Kuhn, causing coach Mike McCarthy to joke that the "Wisconsin diet" must be a factor for the team's spate of hamstring pulls.
There are varying degrees of hamstring injuries. Falcons running back Steven Jackson already missed one game and could be out a few more. Cardinals wide receiver Larry Fitzgerald played through his the past two weeks, but his production dropped significantly.
Eighteen players listed on last week's injury report had hamstring injuries, including 49ers tight end Vernon Davis, Saints right guard Jahri Evans and Dolphins safety Chris Clemons. Cowboys wide receiver Miles Austin, Bills cornerback Leodis McKelvin, Vikings safety Jamarca Sanford and Jets running back Chris Ivory were added to that group over the weekend.
FOOT: Chargers linebacker Manti Te'o and Steelers running back Le'Veon Bell still haven't made their NFL debuts because of foot injuries. Bill safety Jairus Byrd also missed the first three games with a foot problem, and Falcons linebacker Sean Weatherspoon will miss two months. Broncos left tackle Ryan Clady went down for the season with a Lisfranc tear in his left foot, and Cardinals linebacker Lorenzo Alexander is out for the year because a torn ligament in his right foot.
ANKLE: There were 22 players listed with ankle injuries last week. Falcons wide receiver Roddy White and Jaguars running back Maurice Jones-Drew played through theirs, while Steelers cornerback Cortez Allen, Chiefs tight end Anthony Fasano, Colts safety LaRon Landry and Redskins tight end Fred Davis sat out.
Online: AP NFL website: http://www.pro32.ap.org
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