Niagara Gazette — Coach Doug Marrone said he's being cautious regarding the injury and doesn't want to rush Johnson into action too soon.
Without disclosing the nature of the injury, Johnson would only say he's "getting better.".
Veteran defensive tackle Kyle Williams has also not practiced, and is recovering from having offseason surgery to correct a foot injury. It's unclear whether the injury is to the same left foot which Williams had surgically repaired midway through the 2011 season.
Williams said it's still too early to determine whether he'll be cleared by the time the Bills close their series of spring practices with a mandatory minicamp that runs June 11-13.
"I don't know. We've still got a few weeks," Williams said. "We'll see."
The Bills are off until Monday, when they open a three-day voluntary camp.