Source: Joe Walker has torn ACL

Philadelphia Eagles rookie linebacker Joe Walker tore the ACL in his left knee Thursday night against the Pittsburgh Steelers, a source confirmed to ESPN's Adam Caplan.

The Philadelphia Daily News was first to report Walker's injury Friday.

The seventh-round pick out of Oregon has impressed Eagles coaches this summer and was a good bet to make the team's 53-man roster, particularly given the lack of proven depth behind starters Jordan Hicks, Mychal Kendricks and Nigel Bradham.

Walker reportedly "felt a pop" in the knee when trying to make a tackle on a kickoff at the end of the opening half. An MRI this morning showed an ACL tear but no other damage, the source told Caplan.

Looking to bolster the position, the Eagles have been in negotiations, according to ESPN's Adam Schefter, with veteran free agent Stephen Tulloch, who has played for defensive coordinator Jim Schwartz in the past.