The players in the locker room thought Jerod Mayo might have suffered from an ACL or MCL injury. Doctors believe that he might have torn his patella tendon. Regardless, both injuries would sideline Mayo for the rest of the season; the former taking a calendar year to recover, the latter a more manageable six months.
Mayo is the heart of the Patriots defense and Bill Belichick's admitted favorite. He's Tedy Bruschi in the locker and film rooms and he's a leader with his actions on the field. He cannot and will not be replaced. That's asking for the impossible.
Similar to last season, the Patriots will have to adjust to finishing the season without Mayo available. Unlike last season, the depth at linebacker doesn't exist. There's no Brandon Spikes or Dane Fletcher available to help pick up the slack; it's just Jamie Collins and Dont'a Hightower, the latter of whom is still working on returning from an injury.
There are two ways for the Patriots to move forward, and you can be certain they'll dip into both wells. The defense can continue to align in the 4-3 front, or it can make a heavy adjustment into the 3-4 front.
The Patriots can play Deontae Skinner at linebacker; he filled in well on Sunday, even though he has room to grow in pass coverage. This would leave the linebackers with Collins (weak side), Skinner (middle), and Hightower (strong side), which is not as bad as it looks. Skinner would come off the field in the nickel package and the team would continue to function.
Another option would be to move Rob Ninkovich back to linebacker. With Collins at weak side, Hightower could move to the middle with the green dot communicator helmet, and Ninkovich could play on the strong side. Of course, this would mean the Patriots need to adjust on the defensive line, and the team seems comfortable playing Dominique Easley at defensive end.
Moving Ninkovich back would mean that a larger and less quick option would have to play defensive end. Whether it's Easley, or rookie Zach Moore, the pass rush will suffer slightly.
While it's not ideal, the Patriots also feel comfortable with their 3-4 front. They featured a front with Chris Jones, Casey Walker, and Vince Wilfork as the defensive linemen, and once Easley is at full health and Sealver Siliga returns from his injury the Patriots defensive line will become a strength. Easley is most effective out of the three-tech, but as he's still recovering and regaining his quickness, perhaps it won't be as much of a loss keeping him on the outside for his rookie season.
Any defensive front with beef like Wilfork (325 lbs), Walker (330), Jones (310), Siliga (325), and the tiny Easley (290) will be stout against the run and eat up blockers to allow the linebackers to attack the backfield.
The linebackers would be Chandler Jones and Ninkovich on the outside and Collins and Hightower on the inside. All four are legitimate pass rushers and all but Chandler are sufficient in coverage. This combination would give Bill Belichick plenty of room for unique pass rushing sets and put all the best defenders on the field.
There's no one on the team who can replace Mayo; it just can't be done. But the Patriots seem to be in a position where they can make the necessary adjustments to remain one of the more competitive defensive units in the league.