Given that, and the fact that the Eagles aren't carrying any fullbacks, it's a virtual certainty that Kelly will keep four tight ends on his season-opening roster, and probably a fifth on the practice squad.
"It's a great offense for a tight end," Clay Harbor said. "It's the kind of system you want to play in. It definitely allows tight ends to make a lot of plays, and that's what tight ends want to do."
Harbor, a 2010 fourth-round pick, backed up Brent Celek the last 2 years. With coach Andy Reid and offensive coordinator Marty Mornhinweg employing more and more two-tight-end sets, he played 34.6 percent of the Eagles' offensive snaps in 2011 and '12.
Had a career-high 25 receptions and two touchdowns last year. His five red-zone catches were the fourth most on the team.
When Kelly replaced Reid in January, it seemed like a good thing for Harbor. And maybe it still will be.
But as the Eagles get ready to open the preseason tonight against the Patriots, Harbor appears to be the odd man out of Kelly's offense. He's the team's No. 4 tight end at the moment, behind Celek and newcomers James Casey and Zach Ertz.
The Eagles signed Casey in March shortly after free agency began. Then they selected Ertz in the second round of the draft in late April.
"It's just a reflection of what we thought of those two guys," general manager Howie Roseman said. "When you talk about James and what he brings on and off the field to a football team, we just thought he was a player who would fit right in with the culture and really help us.
"As for Zach, we didn't go into the draft thinking we were going to necessarily draft him. But we really liked him. When we woke up the next day [after Ertz wasn't selected in the first round], he was another guy that we just felt was a really good fit for our vision of this football team."
The 6-3, 235-pound Casey lined up at both fullback and tight end for the Texans last year. Like Harbor and the rest of the Eagles' tight ends, he has the versatility to line up anywhere in the formation. He caught a career-high 34 passes last season and was a serviceable, if not overpowering, lead blocker on run plays.
The 6-5, 249-pound Ertz doesn't block as well as Celek, Casey or Harbor, but is an advanced route runner who has been impressive in the red zone in training camp, as well as the rest of the field.
"We've talked in general terms about numbers," Roseman said when asked whether the Eagles likely would keep four tight ends. "We just want to be open-minded about the best players and keeping them here, because you want to have some versatility from those guys.
"They all maybe have different strengths and body types."
The 6-3, 255-pound Harbor is the fastest of the Eagles' top four tight ends. He ran a 4.5 40 at his Pro Day workout before the 2010 draft. He has excellent hands - he has only four drops the last two seasons - but doesn't have Celek's physicality or Casey's feel for the passing game or Ertz' route-running skills. Yet.
"I feel like I'm getting better," said Harbor, who was a wide receiver most of his college career at Division I-AA Missouri State. "I feel like I've improved over the first three seasons and am the best player I've ever been, by far, as far as my understanding and confidence level."
Despite the additions of Casey and Ertz, Roseman said Harbor, who will be a free agent after the season, still is very much in their plans.
"He's an explosive player," the GM said. "Being from a small school, when he puts it together, it looks really good.
"The important thing for him is consistency. Because he has the skill set to be a mismatch in the passing game. And he's big and strong enough to block at the point of attack."
Harbor obviously didn't throw a party when the Eagles signed Casey and drafted Ertz. But he didn't sit around feeling sorry for himself, either.
"I approach it the way I always have," he said. "I try to outwork people and go out there and do the best I can.
"We work together as a unit. More guys to learn from. Take pieces of their game, implement them into your own. It makes you a better player.
"James and Zach are great guys, great players. In the long run, it's only going to make us better competing against each other and playing with each other."