The headline on PackersNews is "Harrell's strength may be sapped." It isn't until the sixth paragraph that it is clear what the hell the headline means:
Harrell probably sat out the two minicamps and the OTAs because he is unsigned. Rookies usually get insurance against any injuries suffered during the minicamps prior to signing their rookie contracts, but maybe the cost of insurance was much higher for Harrell due to his preexisting injury. Since he wouldn't gain much from actually participating, and his spot on the roster is guaranteed, there probably was no reason to take the risk. He just participated in all the classroom activities and got a feel for the defense.
The beat writers gotta love having rookie free agent DE Larry Birdine around. He gave Tom Pelissero some good quotes contradicting Harrell's claims that the injury isn't a problem. Birdine has a history of running his mouth off, such as the time he said USC QB Matt Leinert was "the overrated quarterback for an average offense" before USC went on to pound Oklahoma 55-19 in the national championship game after the 2004 season. Maybe that was bad karma for Birdine because he played very little afterwards in 2005 and 2006 due to injuries.