HAD IT HAPPENED in the season opener, most Eagles fans would have barely shrugged. But Monday, when the team announced that Jordan Hicks would go on season-ending injured reserve after tearing his left pectoral tendon Sunday night, it cast a pall over the Birds' overtime victory in Dallas, and brought into question whether the defense can adequately replace Hicks' heady, difference-making play.

Hicks took the field only on special teams that opening night in Atlanta. He'd impressed teammates and coaches in training camp as an especially smart, fast, tough, intuitive rookie inside linebacker, but Hicks was stuck behind three really good players - DeMeco Ryans, Kiko Alonso and Mychal Kendricks - at the team's deepest position.

Since then, those three really good players have all missed significant time with injury, and late in regulation Sunday night in Dallas, Hicks was polishing his push for NFC defensive rookie of the year. On the national broadcast, Al Michaels and Cris Collinsworth were raving about the play and leadership of Hicks, a third-round rookie from Texas who'd jumped a route and taken a Matt Cassel pass 67 yards for a touchdown early in the fourth quarter.

Hicks said it was the first pick-six of his career, at any level. In previous games he'd managed three fumble recoveries, a sack, a forced fumble, and an INT.

Then, with Dallas driving for the field goal that would force overtime, Hicks reached out to snag pesky Cowboys receiver Cole Beasley, as they crossed at high speed, Beasley having just made the last of his nine catches for 112 yards, on a slant. In yanking down Beasley, Hicks seemed to get his left hand stuck on Beasley's shoulder pad.

Hicks immediately began pounding the turf and waving to get a sub into the game; the Eagles had to take a timeout, with 52 seconds remaining in regulation, to get him off the field.

After Sam Bradford and Jordan Matthews won it for the Eagles in overtime, Hicks was upbeat in the locker room, talking about how nice it was to be back in Dallas, on a field where he and his Longhorns played UCLA last season.

"It was my pec. We'll see what happens. I feel pretty good. I'm not sure what the extent is. We'll see," he said.

Monday afternoon, reporters encountered Hicks again, walking into NovaCare with a big envelope from the Rothman Institute at Jefferson, which is homefield for the Eagles' orthopedists. Hicks said the injury felt better than it had the night before. He was going to get his MRI read, he said.

Within a few hours, the announcement came that ended the most promising rookie season of any Eagles linebacker in recent memory, the rookie the team calls "Simba" to Ryans' "Mufasa." Over the last six games, Hicks played 399 of a possible 434 snaps. Much of the conversation last week concerned how he had proved he deserved to retain a role even as Kendricks, Alonso, and soon, presumably Ryans return to the lineup.

Surgery probably will be needed, but Hicks should be fine for next season, though it might be worth noting that analysts had him as a fourth- or fifth-round draft projection because he'd missed much of two seasons with an Achilles' tear and a hip flexor injury, before finishing with a healthy 2014.

The Eagles filled Hicks' roster spot with Emmanuel Acho, a fellow ex-Longhorns linebacker who was waived with an injury settlement near the end of camp. Acho, who played in 20 Eagles games in 2013 and '14, tweeted, "Guess who's back, back again!" Later Monday evening, the Eagles made Acho's return official.

Eagles coach Chip Kelly spoke with reporters Monday before Hicks and his MRI entered the building; Kelly had no update on any of the injured Eagles, including Ryans, who has missed the last two games with a hamstring problem.

Ryans traveled with the team to Dallas, and, after the game, he lauded Hicks' play. "Jordan is a great player. He stepped in, huge play with a pick-six, a route we talked about all week . . . He is an outstanding player."

Defensive end Fletcher Cox said in Dallas that Hicks "is just stepping up and playing big time, ever since he rolled in."

In the Eagles' Week 2 loss to the Cowboys, it was Hicks who sacked Tony Romo, breaking the Dallas quarterback's collarbone. The loss to the Eagles Sunday was the Cowboys' sixth in a row since. Some Dallas fans exulted over Hicks' injury on social media.

Blog: ph.ly/Eagletarian