In the last four seasons, teams that keyed on Jackson needed to worry about Maclin. Although Maclin was never a 1,000-yard receiver, he had at least four catches in 71 percent of his career games and topped 50 yards in 59 percent of his career games.
Kelly dismissed a question about how much the Eagles miss Maclin because the coach said he believes it's counterproductive to worry about unavailable players. Plus, this offense never had Maclin in the first place.
But the Eagles' Week 3 loss to the Chiefs was discouraging for the passing game because Kansas City's defense appeared determined to keep Jackson from beating it. Jackson was limited to three catches after having 16 in the first two games, and the offense netted 167 passing yards after averaging nearly 360 passing yards in the first two weeks.
"A lot of times, guys are focusing on myself . . . doing some big things in this offense obviously caused that," Jackson said. "I understand at times I might run a certain route and have two guys on me instead of one. I just think that's going to help it out for the other receivers out there."
Jason Avant has been productive from the slot, but Riley Cooper has been a limited threat in the passing game, and new tight ends Zach Ertz and James Casey have seldom joined Brent Celek on the field.
The issue with Ertz and Casey is the way Avant and Celek have played. The coaching staff sees the veterans as two of the most dependable players on the roster, and it shows in playing time: Avant has played 83 percent of the snaps, and Celek has played 88 percent.
Ertz, a second-round pick, has been limited to 25 percent of the snaps, and Casey has taken just 4 percent. Jeff Maehl and Damaris Johnson, the other two wide receivers, have just 13 snaps between them.
"Who are you going to take off the field?" Ertz said. "There's a lot of playmakers, and there's only a certain amount of people you can get on the field at once."
One answer could be Cooper, who has played 97 percent of the Eagles' snaps - the most of any receiver on the roster, Jackson included. Yet Cooper has just six catches for 68 yards and one touchdown in three games.
Kelly defended Cooper on Thursday, saying that Cooper has done "an unbelievable job," and singled out his blocking and his ability in the red zone. He also said a receiver can catch only what's thrown in his direction, although Cooper has caught just six of the 16 passes intended for him this year. Kelly said only one of those passes was a drop.
Some of the responsibility falls on quarterback Michael Vick, who threw an interception on a pass intended for Cooper. But it's also up to Cooper to get open. Kelly said Cooper has created separation and provides more than downfield blocking.
Avant, who is second on the team with 11 catches for 139 yards and one touchdown, said defensive attention on Jackson does not preclude Jackson from having his normal influence in the game.
"Guys are doing a good job to get open, and it's not like we're losing games because Jeremy's not out there," Avant said. "It definitely hasn't been the case. We've lost the games because we've lost them, and there's other areas you look to."
When Kelly praised Broncos quarterback Peyton Manning, he made a point of noting all the weapons Manning has at his disposal. Denver has four receivers with more than 190 yards - the Eagles have just one - and their top receiver has just 26.8 percent of the passing yards.
The Broncos allow 327 passing yards per game, so there could be opportunities for Cooper, Avant, and Celek. Jackson could also have a big game, and he'll play against former Eagles cornerback Dominique Rodgers-Cromartie, who has impressed in Denver after two inconsistent seasons in Philadelphia.