The Eagles used the 13th and 37th picks in April's NFL draft to bring in two highly regarded rookies who were supposed to bolster the defense.

But as the team heads toward the playoffs, the Eagles who were drafted 220th and 244th will have key roles for a defense that still needs improvement, particularly against the pass.

Safety Nate Allen - the smooth player taken 37th - went on the injured reserve list Tuesday after tearing a right knee tendon against the Giants. He joined top pick Brandon Graham, lost the week before to a torn right knee ligament.

Allen will be replaced by seventh-rounder Kurt Coleman.

Middle linebacker Jamar Chaney, drafted 220th overall, also has stepped into a prominent role, taking over as the defensive signal-caller for Stewart Bradley, who is out with a dislocated elbow.

Chaney and Coleman, drafted 11th and 13th, respectively, by the Eagles, have had their moments, and both played big roles. Chaney recorded 16 tackles or assists and Coleman had a key blitz late in the Giants game to force a punt. But they also have shown liabilities, particularly against the pass.

"All of our young guys are doing a good job. Are we leaving some plays on the field from an experience standpoint? Yes," defensive coordinator Sean McDermott said after the Giants game. "We've got to keep working on hammering those out or minimizing those. Those are going to happen when you have young players. But . . . I'm certainly happy with the end result."

Coleman, in spot duty and one start, has been strong against the run, sometimes going onto the field in place of cornerbacks in running situations. But he has been beaten deep several times this year.

Chaney also made his biggest impact while attacking the Giants' runners. But he had his most glaring struggles while chasing tight end Kevin Boss.

Coleman said the young players are confident.

"Seventh round is just a starting spot," he said. "I think that everyone [the Eagles] picked up, they're ready to play. We're good enough to play in this league, and now we're showing it."

Chaney has been active in every game since Week 2, mostly on special teams. Coleman has played in every game this season, with one start, against the Redskins Nov. 15.

The two seventh-rounders are part of a defense that also starts seventh-round pick Moise Fokou at linebacker and undrafted players Quintin Mikell at safety, Dimitri Patterson at cornerback, Juqua Parker at defensive end, and Antonio Dixon at defensive tackle.

Patterson, Fokou, and Dixon had never been regular starters until this year.

"These guys are scrappy guys. They'll battle you, and that's what happened" against the Giants, coach Andy Reid said.

But the defense's liabilities also helped dig the hole at the New Meadowlands. Eli Manning's four touchdown passes left the Eagles with 30 against them for the season. Only the Cowboys and Texans, who have each given up 31, are worse.

The Eagles lead the NFL with 23 interceptions, helping prevent the damage from being worse, but still are giving up points.

In part, that's because they have gotten to the quarterback less, recording five sacks in the last three games, down nearly a sack per game from their previous average.

"It all starts with the defensive line and the offensive line, and the more pressure you put on the quarterback, the better everybody looks," Reid said. "We have to do a better job up front and get it done better."

The Eagles' top two picks were supposed to help do that: Graham by getting into quarterbacks' faces, Allen as a last line of defense against big throws. The defense will have to do without them now.

Contact staff writer Jonathan Tamari at 215-854-5214 or jtamari@phillynews.com. Follow him on Twitter at www.twitter.com/JonathanTamari.