GREEN BAY -- As Mike McCarthy determines which of his rookie running backs can play all three downs, the blitz pickup drill against the linebackers that began in the first padded practice on Saturday is crucial teaching time.

In the drill, the blitzing linebacker and protecting running back are isolated one-on-one. It's sink or swim. But it's not a haphazard, all-out exercise. There's a way to execute the drill that helps both players hone their skills in a useful manner. McCarthy was watching the drill closely on Saturday.

"It’s a good drill, and you want to make sure it gets off on the right foot," McCarthy said on Monday morning, suggesting there's plenty more of it coming. "That drill, if it’s not done properly, you’re teaching bad habits. The depth of the linebacker on the cadence and the depth of the running back is important. (It's a) realistic situation you're trying to create for each guy. If it isn’t realistic, then the technique you're practicing is not what you're looking for."

The Packers have five rookie running backs -- three draft picks plus two undrafted free agents -- along with relatively new starter Ty Montgomery, all working on a skill that isn't easy to master, and protecting QB Aaron Rodgers is a crucial responsibility.

"You want to see the young guys stick their nose in there," McCarthy said. "It's a drill you can’t do enough of, and this is the time of year to do it."

Players had Sunday off and returned to the field Monday morning for another full-pads workout.

Rookie third-round draft pick Montravius Adams, a defensive lineman from Auburn, is out with a foot injury and McCarthy said it will be "multiple weeks" before he returns. Fourth-round pick and pass-rusher Vince Biegel also remains out following offseason foot surgery, leaving the Packers without two of their top four draft picks in the early stages of camp.

"I don’t think it's time for concern. It's an unfortunate part of our game," McCarthy said. "When it happens to young guys, these practices are so critical for their development, especially in Year 1, not only learning what to do and how to do it, but how we practice, everything that goes into it."

Packers.com will have more following practice and locker room interviews.