Tight end Rob Gronkowski tore the ACL and MCL in his right knee during the New England Patriots' 27-26 comeback victory Sunday over the Cleveland Browns, a league source told ESPN NFL Insider Adam Schefter on Monday.
He was officially placed on season-ending injured reserve Monday afternoon. The Patriots signed tight end D.J. Williams, who they released last week, to fill Gronkowski's roster spot.
Gronkowski suffered the injuries in the third quarter after hauling in a pass up the seam from Tom Brady. The two-time Pro Bowl tight end took a direct hit to his right knee from Browns safety T.J. Ward and fell to the ground, clearly in pain.
Brady said Monday the Patriots' formula at tight end must shift without Gronkowski.
"You just have to find a different formula," Brady told the "Dennis & Callahan Show" on WEEI sports radio in Boston, when asked whether the team's other tight ends are capable of doing what Gronkowski does. "I think that's the important part. And Gronk provides a certain margin of error because of how talented a player he is, and the other guys play different roles for us."
Running back Shane Vereen, who had 12 catches for 135 yards (a franchise all-time best for a running back) Sunday, figures to be more of a focal point in the passing game with Gronkowski out.
"I think we'll be able to stay very similar," Vereen said. "Of course, we're going to have to adjust some things but I can't tell you everything we're going to have adjust; we don't have the game-plan for this week yet. We're all going to have to step up, we're all going to have to take on bigger roles."
The Patriots have two other tight ends on the roster, veterans Matthew Mulligan and Michael Hoomanawanui, who missed his third straight game Sunday. In addition, fullback James Develin has taken snaps at tight end on an as-needed basis.
"Those roles are going to have to shift, kind of what we did on the last two drives of the game," Brady said. "We had four receivers at points, at different points we had more [tight ends] with Develin and Mulligan on the field."
"I don't think too many teams have players of that caliber at any position to put in another Rob or another Vince Wilfork or another Jerod Mayo," he said. "Whoever is in there is going to have to fulfill some of those duties, but it may expand to more people, like we ended up having to do [Sunday] offensively. More four-receiver sets, three receivers and a tight end, or something like that. Or it might result in the tight ends getting more plays, or some combination thereof.
"However that may be, it may change from game to game. Obviously we, unfortunately, had to play without Rob for [six] games at the beginning of the season. We may be in that situation again. We dealt with that already this year."
Ward said Sunday he targeted Gronkowski low due to a fear of being fined by the NFL.
"It was a decision I made just to make a tackle on a big man, and unfortunately he got hurt," Ward said. "But if I would've hit up high, there's a chance I would get fined and all that other stuff. I'm just being safe."
Medical personnel immediately came to Gronkowski's side, and he was eventually taken off the field on a cart. He was unable to put weight on his right leg as he moved from the ground to the cart.
"My intention is never to hurt anyone," Ward said. "That's not what this game is about. That's not how I play. I hate to see guys go down with any type of injury and I just wanted him to know, whether he accepted it or not, it wasn't an intentional hit to injure him. But we have to play this game, we have to play it the way that they force us to, and unfortunately, we incurred an injury for him."
The 24-year-old Gronkowski missed the first six games this season while recovering from offseason back and forearm surgeries. He thrived in the next six games, catching 37 passes for 560 yards and four touchdowns.
The Patriots scored the second most points in the league during the six games he played before Sunday. They had the 22nd-best scoring offense in the league without Gronkowski.
Belichick said Monday he's hopeful the Patriots (10-3) will be able to draw on what they did earlier this season without Gronkowski in the lineup.
"I'd like to think there's going to be some carryover there. Not only [was] it the first six weeks of the season, but the entire training camp as well. I think that's the way we practiced and played most of the year, including the preseason, that's 10 games," he said.
"It was great to have him back and he was obviously a big contributor for us because he's an outstanding player. I hope that his situation isn't as serious as what it might be, but if it is, then I'm sure it'll be some combination of what we've already done this year, or maybe because we have a few different players and we're at a different point of the season, it may be some different things, too."
Signed to a lucrative contract extension during the 2012 offseason, Gronkowski has become a centerpiece of the Patriots' offense. He set an NFL record for tight ends with 17 receiving touchdowns during the 2011 regular season.
ESPNBoston.com's Field Yates contributed to this report.