The NFL has said the four linebackers being investigated for an alleged link to performance-enhancing drugs will be suspended if they don’t agree to be interviewed by the league in the next 10 days.

NFL senior vice president of labor policy and league affairs Adolpho Birch sent a letter Monday to the NFL Players Association detailing the plan to suspend James Harrison of the Pittsburgh Steelers, Clay Matthews and Julius Peppers of the Green Bay Packers and free agent Mike Neal if they don’t speak with the league by Aug. 25. Their punishment would start the following day.

RAVENS: Outside linebacker Terrell Suggs returned to practice for the first time since tearing his left Achilles tendon last September.

The six-time Pro Bowl selection participated in Monday’s workout on a limited basis. He said in a statement: “It felt great to be back on the field with the team, there is nothing like it. Didn’t get to do too much today as I am working my way back.”

BILLS: Buffalo will release defensive end IK Enemkpali after he sustained a season-ending injury to his right knee.

The Bills placed Enemkpali on their waived/injured list, shortly after Coach Rex Ryan said Enemkpali has a torn a ligament in his right knee.

The move freed up a roster spot for Buffalo to sign linebacker Kroy Biermann and address its injury-depleted pass-rushing depth. Biermann is a free agent who spent his first eight seasons with Atlanta.

VIKINGS: Coach Mike Zimmer has left open the possibility of some preseason playing time for running back Adrian Peterson.

Zimmer said he has not decided whether or not to put Peterson on the field in an exhibition game for the first time in five years. Zimmer said he’d let Peterson play “if he wants to,” but the coach and the player have not discussed the situation recently.

SAINTS: Defensive tackle and first-round draft choice Sheldon Rankins has been diagnosed with a broken fibula, an injury that occurred during training camp practice in West Virginia, a person familiar with the situation told the Associated Press.

The person, who spoke to the AP on condition of anonymity because the Saints haven’t disclosed Rankins’ injury, said Rankins is seeking a second opinion but appears to need surgery. Typically, fractured fibulas are not season-ending but sideline players for about six weeks.

COWBOYS: Dallas signed Pro Bowl center Travis Frederick to a six-year, $56 million extension that runs through 2023.

The average of $9.1 per season makes him the NFL’s highest-paid center.

BRONCOS: Defensive end Vance Walker injured his right leg on the second play of 9-on-7 drills. He was driven to the entrance of the Broncos’ facility and couldn’t put any weight on the leg as he was helped into the building.

Walker is listed as one of the starting defensive ends on the team’s depth chart. He is expected to step into a starting role after Malik Jackson signed with Jacksonville in the offseason.

LIONS: Detroit signed free agent tight end Andrew Quarless, who is facing a two-game suspension to start the season.

Quarless was suspended two games for violating the league’s personal conduct policy but is eligible to participate in preseason games. Quarless was sentenced to a year of probation and fined $1,000 for firing a gun in Miami Beach, Florida.

SEAHAWKS: Former Seattle safety Kenny Easley has been selected as the senior finalist for the 2017 Pro Football Hall of Fame class.

Easley was the No. 4 overall pick in the 1981 draft and played seven seasons, all in Seattle. He was a first-team All-Pro four straight years from 1982-85 and was the NFL defensive player of the year in 1984, when he led the league with 10 interceptions, two of which he returned for touchdowns.