After making a 4-yard catch, Boyle took a direct hit on his left leg, causing it to bend inward. Patriots linebacker Terez Hall's right shoulder went right into the side of Boyle's knee, and both Ravens and Patriots players immediately signaled for trainers to come out onto the field.
The entire Ravens team surrounded Boyle before he was carted off the field.
"Nick is our brother," Baltimore quarterback Lamar Jackson said. "We were hoping he would just be out for the game at least. But [we're] just finding out he's out for the season. I don't even know what to say. [I'm] ticked off."
Boyle is considered one of the top blocking tight ends in the NFL. He entered Sunday's game as Baltimore's sixth-leading receiver.
"It's hard to really quantify what Nick does for us as an offense and as a team," said Ravens tight end Mark Andrews, who is a close friend of Boyle's. "He's a person that people gravitate towards. For me, he's meant a ton to me, and it sucks. It sucks for him; he's worked so hard to get to where he's at."
Williams injured his left ankle early in the game and was initially considered questionable before being downgraded.
The Ravens were already without defensive end Calais Campbell, who was inactive with a calf injury. It ended Campbell's streak of 98 straight starts, which was the second longest current streak for defensive ends.
Without Williams and Campbell, Baltimore allowed 173 yards rushing in the loss. The Ravens had entered Sunday night with the No. 8 run defense, giving up 101.8 yards rushing per game.
For the Ravens' offense, this was the second time in three games it lost a starter to a season-ending injury. On Nov. 1, All-Pro left tackle Ronnie Stanley was lost to an ankle injury.
"Everyone in this locker room loves him to death, and he's one of the most loved people on this team," Andrews said of Boyle. "We're going to miss him dearly. We know he has our backs, and we have his. It's just sad. It's sad to see."