The nature of his illness is unknown at this time, but it's not regarded as serious.
Practice was closed to reporters Thursday at McDaniel College.
Meanwhile, cornerback Fabian Washington (knee) has passed his physical and has been activated from the physically unable to perform list.
Washington has made a rapid recovery from a torn anterior cruciate ligament suffered last season.
"It really felt good running around with the guys again," Washington wrote on his Twitter acount. "The knee feels great."
Undrafted rookie wide receiver Rodelin Anthony (knee) also passed his physical.
Heap placed on non-football illness list
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