Hightower is scheduled to visit Dr. James Andrews on Thursday, a source told ESPN's Adam Schefter. And while sources say Hightower's season is over, the Patriots are still uncertain he will be out for the year, another source told ESPN.
On Wednesday, the Boston Herald reported that the Patriots would be without Hightower for Sunday's game against the Los Angeles Chargers. On Thursday, multiple reports emerged saying Hightower's prognosis was worse and that he would miss the rest of the season.
Hightower was hurt in last Sunday's 23-7 win over the Atlanta Falcons while tackling running back Devonta Freeman with 3:04 left in the third quarter. Hightower remained down briefly after the play, clearly in pain, but he stayed in for the next snap, a running play in his direction. He then came off the field for the remainder of the game and watched from the sideline.
The 6-foot-3, 265-pound Hightower missed games in Weeks 2 and 3 with a knee injury sustained in the third quarter of the season opener. Upon his return, he was used in a part-time role, playing 37 snaps in an Oct. 1 loss to the Carolina Panthers before seeing his workload increase to 62 and 69 snaps, respectively, over the next two games.
He has been credited with 14 tackles and two sacks this season.
In his absence, the Patriots have Kyle Van Noy, Elandon Roberts, David Harris, Marquis Flowers and Trevor Reilly on their off-the-line linebacker depth chart. Roberts missed the win over Atlanta with an ankle injury. Four-year veteran Van Noy has played 95.3 percent of the defensive snaps, the most at linebacker for the Patriots this season.
"That's terrible news for a guy like Hightower to go down with that injury and to be out for the year," Harris said. "What he means to this defense, knowing the defense like the back of his hand, to lose a guy like that is a huge blow for the team. ... As a linebacker group, we have to try to fill his place, which is going to be tough to do."
Safety Devin McCourty called the injury a big blow to the Patriots but said the team has to push on.
"He's a huge part of what we do," McCourty said. "We've been out there a couple games without him, so we know what that is like. It's always the same thing: When a guy like that goes down, a bunch of guys have to step up and try and fill that role, and in this case, a bunch of different roles. It is something we'll have to overcome."
Six-year veteran Shea McClellin, who opened the season on injured reserve, is eligible to return to action Nov. 12 against the Denver Broncos and should elevate to the upper parts of the depth chart quickly.
Hightower was one of the top unrestricted free agents this past offseason. After taking visits to the New York Jets and Pittsburgh Steelers, he returned to the Patriots on a four-year contract that included a $10 million signing bonus. In part because he had been in and out of the lineup due to injuries, the deal included per-game roster bonuses of $54,687, which is a higher figure than the norm.
A defensive captain, Hightower's versatility to play an off-the-line linebacker role, or on the line at the end of the line scrimmage, is valued by the coaching staff. His knowledge of the defensive scheme and experience was cited by players as having a calming effect on the unit.
ESPN's Mike Reiss contributed to this report.