Eagles linebacker Jordan Hicks will miss the remainder of the season with a torn left pectoral tendon, a devastating injury for a rookie who emerged from a reserve role to become one of the most productive players on the team.

Hicks was hurt Sunday in the fourth quarter of the Eagles' 33-27 win over the Dallas Cowboys. An MRI exam on Monday afternoon revealed the damage, and the 23-year old will need to go on injured reserve.

The injury comes at a position in which the Eagles have unusual depth, although their top players have struggled to remain healthy. The Eagles are now left splitting playing time with the same trio Hicks was set to back up this season: Kiko Alonso, Mychal Kendricks, and DeMeco Ryans. Ryans has missed the last two games with a hamstring injury, but he is expected to return soon.

The Eagles will replace Hicks with veteran Emmanuel Acho. Acho spent the last two years with the Eagles before the team reached an injury settlement with him during training camp. Acho knows the defense and also can contribute on special teams. The signing was not yet official on Monday evening.

Alonso and Kendricks have missed time this season, and their absence was not as costly because of Hicks' emergence. Hicks finished his rookie season with 50 tackles, one sack, two interceptions one forced fumble, three fumble recoveries, and a touchdown.

The Eagles were scrutinized in the spring when they drafted Hicks in the third round out of Texas. It's a position in which they had depth, and Hicks was not considered a top prospect. But the Eagles had more exposure to Hicks than any player available, and they maintained conviction about the linebacker who quickly proved he was mature beyond his experience.

Hicks started playing on defense in Week 2 against the Cowboys. He sacked Dallas quarterback Tony Romo, who fractured his clavicle on the play. Hicks further hurt the Cowboys on Sunday when he returned an interception 67 yards for a touchdown.

In between, Hicks was dependable and productive to the point that the team was committed to keeping Hicks in the inside linebacker rotation even when the three veterans were healthy.

"In the beginning of the year, he wasn't in the conversation other than special teams and a backup role as we grew him," defensive coordinator Bill Davis said. "But he jumped in and did such a nice job that now he has brought himself into the conversation of a main rotation."

He drew comparisons to Ryans, who is one of the most respected players in the locker room. In fact, teammates started calling Hicks "Simba" because coach Chip Kelly had called Ryans "Mufasa." Simba is the son of Mufasa in The Lion King.

Without Hicks, the Eagles need their established linebackers to remain healthy and play to their potential. Ryans and Kendricks were productive players in the defense during the last two seasons, and the variable is Alonso. The Eagles acquired him from the Bills for LeSean McCoy in March, but he has spent more time on the sideline than the field. Alonso returned on Sunday for the first time since Week 2 and played 37 percent of the defensive snaps. Hicks and Kendricks both played 72 percent of the snaps.

"I thought Kiko played well," Kelly said. "I know those guys were pleased. It's his first time back since I think the last Dallas game. We also knew we got to ease him into this thing; you can't just continue to throw him out there and then all of a sudden we lose him.

"They were pleased with how he played in terms of how [inside linebackers coach] Rick [Minter] graded those guys out at inside linebacker, so we'll see if we can build on that for him."

The Eagles also have Najee Goode and Brad Jones at inside linebacker, so there is depth at the spot beyond the top three players. But they no longer have Hicks this year in a case of gloomy news hours after he starred in the Eagles' victory.

zberman@phillynews.com

@ZBerm