FOXBOROUGH, Mass. -- Tom Brady will miss the entire NFL season with a left knee injury that will require surgery, leaving the New England Patriots without one of the game's great quarterbacks and their Super Bowl hopes severely damaged.
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."
The Patriots brought in free-agent quarterbacks Chris Simms and Tim Rattay on Monday, but once they arrived they were told the situation had changed and that they were no longer neeeded, reports NFL Network's Adam Schefter. Kansas City and Tennessee, each of whom had quarterbacks suffer significant injuries on Sunday, also have contacted Simms, Schefter reports.
Belichick 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."
"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.
Cassel, who was a backup at Southern California to Heisman Trophy winners Carson Palmer and Matt Leinart, is the starting quarterback for now.
"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.
The league said the play was reviewed by Mike Pereira, the supervisor of officials, who determined it was legal.
"It is not a foul because the defensive player was coming off and affected by a block by the offense," NFL spokesman Greg Aiello said.
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.
A former fourth-stringer who was the 199th overall selection in the 2000 draft, Brady himself took over at quarterback when longtime starter Drew Bledsoe sustained a life-threatening chest injury in a 2001 game against the New York Jets. Brady led the Patriots to their first NFL title that year, another in 2003 and another in 2004.
But he missed the entire 2008 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."
The Associated Press contributed to this report