A towel covered Maclin's face while he lay with his right foot extended on the cart, concealing the agony Maclin no doubt was experiencing. He tore the same ACL as a freshman at Missouri in 2006, and has dealt with injuries throughout his four seasons with the Eagles.
Kelly was not available for comment Saturday night.
"Usually when a guy goes down like that it's something to worry about," Vick said after practice.
The injury is especially devastating because Maclin, who was entering the final year of his contract, was expecting the best season of his career. A first-round pick who has been a four-year starter with the Eagles, the 6-foot, 198-pound receiver has been a consistent contributor although he never exceeded 1,000 receiving yards in a season. He has more catches through his first four years than any player in Eagles history.
He said this summer that he was not in a rush to pursue a contract extension because he "can only get better." He was going to be a featured part of Kelly's system, and came to camp healthy and eager to fulfill the potential the Eagles saw when they drafted him in 2009.
When he reported last week, he said he was aware of the contracts other wide receivers around the league had received. Maclin would have been in line for a lucrative deal with a strong 2013 season.
The injury leaves the Eagles looking for a starting receiver. Riley Cooper took the first-team snaps in Maclin's place Saturday. Cooper made 23 catches for 248 yards and three touchdowns over 11 games last season.
At 6-foot-3 and 222 pounds, he presents a big, physical threat, but he lacks the speed and experience typical of a featured receiver.
"I think during OTAs and minicamps, I think overall I had a good camp," Cooper said. "I feel like I'm fitting in. I'm a big body, so that's a little different. But the whole blocking-scheme stuff and blocking the perimeter and the bubble screens we run, I can do that. That's a strength of mine."
The Eagles likely will not move Avant from the slot, where he has played most of his career. Other options with NFL experience on the roster are Damaris Johnson and Arrelious Benn. Johnson, who is 5-foot-8, does not have the size to compensate for Maclin's loss. Benn, who is 6-foot-2 and 220 pounds, is a former second-round pick with potential, but injuries have derailed his career. He suffered a knee injury Friday.
The other receivers on the roster are Russell Shepard, Ifeanyi Momah, Greg Salas, Will Murphy, and B.J. Cunningham. Momah, who is 6-foot-7 and 239 pounds, has impressed the coaches. Shepard caught Vick's eye during the first week. Expect the Eagles to play multiple tight-end sets, so Zach Ertz and James Casey will be split out as wide receivers.
The Eagles could pursue a free-agent receiver or trade for one, but it will be hard to find a quality replacement at this point. The top free agent on the market is Brandon Lloyd, who had 911 yards last season with the Patriots.
But pressure is also on DeSean Jackson, who has combined with Maclin during the last four seasons. Jackson has not exceeded 1,000 yards the last two years, but he will be the undisputed No. 1 receiver in Maclin's absence.
"He takes the pressure off myself. He's able to go out there and make big plays, just like myself," Jackson said. "Whenever you have a guy like that who can release guys from a double team and triple team, that's a super-huge addition."
How they fill the void will be determined in the coming days. On Saturday, though, the Eagles needed to come to grips with the fact that one of their most productive offensive players has been lost. And Maclin was left with the reality that a season so pivotal for his future ended on the practice turf before he even played a game.
Contact Zach Berman at firstname.lastname@example.org. Follow on Twitter @ZBerm.