Cowboys on verge of signing Toby Jackson

OXNARD, Calif. -- The Cowboys are on the verge of signing defensive end Toby Jackson, according to a source.

Jackson was one of four players to work out with the Cowboys on Tuesday afternoon.

Jackson didn't play football at the University of Central Florida last year because of academic issues. He was available in this summer's NFL's supplemental draft but wasn't selected.

To make room for Jackson, the Cowboys would have to make a roster move.

The defensive line has battled through several injuries during training camp. The Cowboys currently are without Cameron Sheffield (groin), Ike Ikponmwosa (leg), Jay Ratliff (hamstring), Landon Cohen (eye), Anthony Spencer (knee) and Tyrone Crawford (Achilles).

Crawford will miss the season, but Spencer should return by the regular-season opener. Ikponmwosa, Sheffield and Ratliff will miss a few more weeks, while Cohen should return for Thursday's practice.

The Cowboys want to add a defensive lineman, but another roster move could occur depending on the severity of right guard Kevin Kowalski's leg injury. Kowalski went down during two-on-two pass-rush drills on Tuesday afternoon and missed the last 30 minutes of practice.

If Kowalski misses an extended period of time, the Cowboys could add another offensive linemen in addition to the defensive linemen being pursued.

UPDATE: The Cowboys released defensive tackle Ikponmwosa Igbinosun and signed rookie free agent DE Toby Jackson out of Central Florida.

The Cowboys didn't practice Wednesday.