CLEVELAND — The Cleveland Browns are awaiting further test results on starting inside linebacker D’Qwell Jackson, who sustained his second chest muscle injury in 10 months.

Jackson was in the midst of a comeback after missing Cleveland’s final 10 games last season with a torn pectoral muscle that required surgery. He injured his other chest muscle during practice on Tuesday, team spokesman Neal Gulkis said.

Gulkis said Jackson has undergone testing and will have more procedures to determine the extent of his new injury. The Browns are not expected to release any results or provide further information until Thursday, when they will also have two practices.

If Jackson’s muscle is torn, he would likely miss the entire season.

Agent Brian Mackler said he was waiting to hear from doctors and had no update.

Denver star linebacker Elvis Dumervil, the NFL’s sacks leader last season, tore a pectoral muscle during camp and is likely to be out for five months.

Browns coach Eric Mangini gave his players a day off from practice on Wednesday, but they reported for meetings, treatment and workouts in preparation for Saturday’s exhibition opener in Green Bay against the Packers.