The 2007 NFL Most Valuable Player will be placed on injured reserve, the Patriots said Monday, one day after his knee was injured in the first quarter of a 17-10 victory over the Kansas City Chiefs.
A statement issued before coach Bill Belichick's news conference said Brady will have surgery, ending his 128-game starting streak, the third longest for a quarterback.
Brady left Sunday's game against Kansas City after he was hit by Chiefs safety Bernard Pollard. Brady was not available for comment, but reports circulated around the league that he had torn his anterior cruciate ligament.
"We feel badly for Tom about the injury," Belichick said while not confirming the exact injury. "You hate to see anyone go down. No one has worked harder or done more for this team than Tom has."
Matt Cassel, who guided New England to its 20th straight regular-season win after Brady was hurt, will start Sunday at the New York Jets.
"As a team we all just have to do our jobs," Belichick said. "That really doesn't change."
But Brady's injury surely changes the complexion of the AFC, where the Patriots, winners of three Super Bowls since 2001 with Brady as their quarterback, were a strong favorite. Cassel's first true game experience came against the Chiefs.
"I'm not trying to be Tom Brady. I'm just trying to be Matt Cassel," he said when subbing for Brady on his regular weekly radio show. "I don't know where that's going to take us."
Cassel, who even was a backup at Southern California -- to Heisman Trophy winners Carson Palmer and Matt Leinart -- could have some competition. A person familiar with the situation told The Associated Press that former Tampa Bay quarterback Chris Simms was heading to Foxborough on Monday for a physical, and reports elsewhere said Tim Rattay was also being considered.
Belichick, who runs one of the most secretive operations in the league, denied the team reached out to any other quarterbacks. "In spite of what some people are putting out there, we haven't worked out anybody," he said. "We had a lot of people call us, I can tell you that."
For now, Cassel is his quarterback.
"The opportunities that Matt got, experience always helps," Belichick said. "I have a lot of confidence in Matt."
Belichick stopped short of calling the hit by Pollard dirty. He did emphasize his players are always taught it's their responsibility to hit the QB above the knees and below the shoulders.
Brady, 31, threw for a record 50 touchdowns in leading the Patriots through a perfect 2007 season to the brink of their fourth Super Bowl title in eight years. But New England lost its chance at an unprecedented 19-0 record when the Giants won the championship, 17-14.
He missed the entire preseason with an unspecified foot injury, then left the season opener 7:33 into the first quarter.
"He was in a lot of pain," Pollard said. "When you hear a scream, you know that."
After being tended to on the field, Brady walked off, limping, between two trainers. He went to the locker room and wasn't seen on the sideline again.
Brady was 7-for-11 for 76 yards, completing a 28-yard pass to Randy Moss on the play in which he was injured. Moss fumbled the ball away when he was tackled; the Patriots forced Kansas City to punt, then Cassel came in for New England.
"Since I've been here and been around Tom, he's always popped back up," Cassel said. "I didn't know (how serious it was). I just buckled my chin strap and the guys rallied around me. I felt their support.
"This is something I've been preparing for a long time. It's not something I expected to come up on opening day."