FOXBOROUGH, Mass. — If the Patriots are going to win a sixth Super Bowl, they’ll have to do it without one of their key defensive pieces.

On Thursday, Dont’a Hightower had season-ending surgery to repair a torn pectoral muscle. The linebacker is expected to be back for the 2018 season, but the news is devastating for a Patriots defense that’s been improving over the last three weeks.

The injury occurred on Sunday night against Atlanta. Hightower was ruled out with a shoulder injury, but on Thursday morning, it was confirmed that the linebacker also suffered a torn right pectoral muscle. The defense will now need to move on without one of their captains and leaders.

“That’s terrible news for a guy like Hightower to go down with that injury and be out for the year,” linebacker David Harris said. “Knowing what he means to this defense, he’s one of the captains to the team and knows the defense like the back of his hand. To lose a guy like that is a huge blow for the team. At the linebacker group, we have to step up and try to fill his place, which will be tough to do.”

Hightower suffered the season-ending injury at 3:06 of the third quarter on Sunday. As running back Devonta Freeman ran up the middle, he cut left. At the same time, Hightower was running to his left, but overcommitted so he reached out with his right arm and fell on his right side. He grabbed Freeman with his right hand, but the back kept moving up field. Immediately, Hightower looked like he was in pain. He stayed in for one more play, but then left the field and was ruled out.

The 27-year-old captain is one of the Patriots best defensive players. He’s by far the Patriots best linebacker and was named to the Pro Bowl and second-team All-Pro last season. That’s one reason why they signed him to a four-year, $35.5 million contract extension in March. The sixth-year veteran, however, has a lengthy injury history..He’s only played a full 16-game season once, but has never played less than 12 games. Unfortunately, for the Patriots, his season ends after playing only five games this season, which he totaled 14 tackles and two sacks.

“It’s a tough loss,” safety Devin McCourty said. “He’s a guy who’s been out there for a lot of years now. Played multiple roles on the defense, different spots. Communication everything, he’s a huge part of what we do. We’ve been out there for a couple games without him. We know what that’s like, but it’s always the same thing when a guy like that goes down. A bunch of guys have to step up and kind of try to fill that role. In this case, a bunch of different roles. It’s a tough loss for us defensively, but it’s something we’ll have to overcome.”

This season, Hightower started at left defensive end. After missing two games, with a knee injury, he was moved back to middle linebacker against Tampa. It was there where the defensive started to turn things around. Multiple defensive players said Hightower’s move back to the middle had a calming effect on the unit.

The team now moves forward with Kyle Van Noy, Elandon Roberts, Harris, Marquis Flowers and Trevor Reilly at the position. Shea McClellin is eligible to come off the injured reserve in Week 10 against Denver.

“I mean, it’s going to take a full unit. Dont’a (is) a special player. He does a lot for this team. It’s going to take a group effort,” said Van Noy. Communication is “definitely getting better. It’s going to take a whole group to do it. He’s a leader of this team and the defense. We know what we have to do to fill his spot.”

In the event the Patriots want more help, the NFL trade deadline is next Tuesday.

“As a team, we’ll always figure it out,” McCourty added. “I firmly believe our coaching staff spends lot of hours figuring out what we need to do personnel wise, who needs to play here. What works, what won’t work. We’ll figure it out. Whether that takes a quarter or two quarters, it’ll happen.”

Danny Amendola returned to practice after missing the previous day’s session because of a knee injury. The Patriots were still without Malcom Brown (ankle) and Eric Rowe (groin).

With the news regarding Hightower, seeing Amendola at practice was a positive sign for the Patriots. Rowe isn’t expected to be back anytime soon, and it’s unknown how long Brown will be out after leaving Sunday’s game because of a lower body injury.

The Patriots added a new practice squad player – receiver Jake Kumerow. The 6-foot-4 undrafted free agent out of Wisconsin-Whitewater spent parts of the last two seasons in Cincinnati, where he was released on Sept. 22.

He’s the cousin of Los Angeles Chargers defensive end Joey Bosa.