3:35pm: Hightower underwent surgery to repair the damaged pectoral muscle on Thursday, Ian Rapoport of NFL.com tweets. Rapoport adds the veteran linebacker is expected to make a full recovery in time for the 2018 season.
10:30am: The Patriots still do not know if Hightower will be out for the year, Adam Schefter of ESPN.com tweets. Hightower will visit Dr. James Andrews to get a better assessment of the damage.
9:51am: Patriots linebacker Dont’a Hightower will miss the remainder of the season with a torn pectoral, according to Ian Rapoport of NFL.com (on Twitter). The Pats are expected to formally place him on injured reserve on Thursday afternoon. 
Losing Hightower is a major blow to the Patriots’ defense. As the team’s middle linebacker, Hightower was essentially the leader of the front seven and the extension of defensive coordinator Matt Patricia on the field.
Hightower missed two of the Pats’ games in September and his absence was noticeable. Heading into Week 4, the usually solid Pats ranked dead last in the NFL in points allowed, yards allowed, and defensive DVOA. They can draw from a reserve group including Kyle Van Noy, Elandon Roberts (missed Sunday’s game with an injury of his own), David Harris, Marquis Flowers, and Trevor Reilly, but it would make sense for them to explore available MLBs between now and the Halloween trade deadline.
Hightower, 27, played in 13 games last season and racked up 65 tackles, 2.5 sacks, and two forced fumbles, ranking as Pro Football Focus’ 12th-best linebacker among 87 qualifiers. In the spring, he was rewarded with a four-year, $43.5MM deal, including $19MM guaranteed. The Patriots’ decision to keep Hightower and re-sign him on a large contract underscored his importance after they traded away other key defenders such as Jamie Collins and Chandler Jones.