GREEN BAY, Wis. -- It wasn’t the ideal preparation for Kenny Clark, but at least it appears the Green Bay Packers' first-round pick will be available for the regular-season opener.

Clark returned to practice Tuesday, the Packers’ first this week in advance of Sunday’s Week 1 game at Jacksonville. It marked his first time on the field since Aug. 22, when his back tightened up during practice. Clark was unable to go the next day, and it was the first time he had ever missed a practice in his football-playing life.

“That was probably one of the most frustrating parts because I’m not out there with my teammates,” Clark said this week. “But I learned from it, and just doing a better job of stretching and doing a lot of stuff to take care of my body.”

Clark said he did not know what caused his back problem.

“I was just out at practice, punched and my back just tightened,” he said.

The defensive tackle from UCLA already was starting from behind because NFL rules prohibited him from joining the Packers’ offseason program until his alma mater was out of session. Because UCLA is on the quarter system, that meant Clark missed about a month of organized team activities before he could finally come to Green Bay in June, even though he was not enrolled in school. He and fellow rookie defensive end Dean Lowry (Northwestern) were in the same situation but kept in touch via Skype with assistant coach Mike Trgovac.

Even with a late start to his pro career and an early end to training camp, Clark likely will have a significant role against the Jaguars. The Packers kept only five defensive linemen. and three of them -- Clark, Lowry and Christian Ringo, who spent all of his rookie season last year on the practice squad -- have never played in an NFL regular-season game. The only two veterans in Trgovac’s room are Mike Daniels and Letroy Guion (Mike Pennel is serving a four-game suspension).

“I’m going to be candid with you: He’s going to have to play,” Daniels said of Clark. “We’re going to need him. That’s why we brought him in. Liked what you saw out of him. Unfortunately he has some issues going on, but we’ll see. But I would love to get him out there. The more experience you get, the better you play, and that’s why they say it’s good to have vets.”

The Packers won’t have to release an official injury report until Wednesday, but the only three players who did not appear to do anything during Tuesday’s practice were outside linebacker Jayrone Elliott, safety Chris Banjo and cornerback Josh Hawkins. Elliott and Banjo both missed the preseason finale because of hamstring injuries. Hawkins’ reason for missing practice was not known.

Receivers Jeff Janis (hand) and Trevor Davis (shoulder) both appeared limited in practice. Janis wore a club-cast on his broken right hand. Packers coach Mike McCarthy said before Tuesday’s practice that Davis would “be challenged to make it this week,” which is usually McCarthy’s code for a player who won’t play.

As expected, Jordy Nelson appeared to practice without limitations a day after McCarthy said his Pro Bowl receiver would be “full bore” for Sunday’s game despite not playing a snap in preseason while recovering from the torn ACL that kept him out all last season.