Coach Doug Marrone said after practice Wednesday that fullback Evan Rodriguez was also treated for the same problem and released from the hospital earlier in the day.
Marrone isn't providing any further details on Gragg's condition or when he was sent to the hospital.
Both players missed the past two days of practice. They last practiced Monday, during a 2 1/2-hour afternoon session in muggy conditions and temperatures in the high 80s in suburban Rochester.
The Bills have a day off before resuming practice Friday.
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