GREEN BAY, Wis. -- Not long after they were drafted this spring by the Green Bay Packers, Kenny Clark and Dean Lowry got a call from the fiery leader of the defensive line.

Mike Daniels was on the phone, and he needed them to get ready quickly.

The Packers will be down a veteran up front early in the season because of the four-game suspension of Mike Pennell, so Clark and Lowry must be ready to play right away. That means there is no time to waste in training camp for the rookies.

More from FoxSports

"I'm not going to lie to you," Daniels said. "We need them ready like yesterday."

After Daniels and Letroy Guion, the Packers will be short on experience up front to start the season.

Veteran B.J. Raji is on a one-year "hiatus" from football. Pennel emerged as a competent backup in 2015, but the third-year player will miss the first four games for violating the NFL's substance-abuse policy. Datone Jones has been moved to a hybrid pass-rushing role in which he'll line up more like an outside linebacker.

Clark, the Packers' first-round pick out of UCLA, could emerge as a starter right away. Lowry, a fourth-round pick from Northwestern, could see significant snaps as a backup.

Coach Mike McCarthy doesn't seem concerned, at least this early in camp. He said he has been satisfied with the progress of his rookies so far since the offseason program. There are five preseason games and to get the young guys in shape.

It's part of the annual shuffling in Green Bay anyway, which surrounds a talented veteran core with a healthy complement of younger players.

Two years ago, the youth was concentrated in the receiving corps; last year, it was cornerback.

This training camp, the defensive line is front and center.

"Let's face it, this game's about big men and the big men have to control the balance of what (happens) on the field and frankly in the locker room, too," McCarthy said. "So the consistency of our young D-linemen will be critical to how that group grows."

In Daniels, McCarthy has an ideal mentor for the rookies. A fourth-round pick in 2012, Daniels has turned into a stabilizing and energetic presence up front.

The Packers held their first practice with pads on Thursday. It had barely started when a brief scuffle broke out during a drill. Not surprisingly, Daniels was right in the middle, mixing things up with an offensive lineman.

"He's naturally aggressive like that," four-time Pro Bowl guard Josh Sitton said. "He's got that leadership quality too where he wants to get other people going. Get other people fired up, too."

For Daniels, the tutoring of Clark and Lowry started months ago, in phone calls to the rookies a day or two after they were each drafted in late April.

"They're not putting any kind of pressure on me. They're just making sure, like, `Man, you need to be solid by Game 1 and we want you to be good,'" Clark said. "I'm taking all of that in. I'm excited for it. I love it."

NOTES: House Speaker Paul Ryan, a lifelong Packers fan, attended practice with his family. The Wisconsin Republican talked football with team president Mark Murphy; met his favorite player, quarterback Aaron Rodgers; and addressed the team at midfield. "Look, I'm used to giving a lot of speeches, I was actually pretty nervous talking to these guys," Ryan said. As just a lifelong Packer fan, it was just a pretty cool experience, just to meet the team." ... The Packers signed WR Harvey Binford on Thursday. Binford played for the Philadelphia Soul of the Arena Football League in 2015-16. ... The team is off on Friday and returns to practice on Saturday.