BOSTON -- New England quarterback Tom Brady will be out for the rest of the season after he injured his knee during the team's opening game, the team announced Monday.

"After extensive tests this morning, it was revealed that New England Patriots quarterback Tom Brady's left knee, which was injured in the first quarter of yesterday's game, will require surgery," the team said in a statement.

Belichick Talks About Brady Injury

Brady, 31, will be placed on injured reserve and will miss the remainder of the 2008 season. The quarterback underwent an MRI at Massachusetts General Hospital to determine the extent of his knee injuries.

"We feel badly for Tom about the injury. You hate to see anyone go down. No one has worked as hard and done more for this team than Tom has, so it is a tough setback," Patriots Coach Bill Belichick said Monday afternoon.

Belichick denied reports that the team was "working out other quarterbacks" to replace Brady. The coach said they would "evaluate the options and do what is best for the team."

"We haven't worked out a quarterback or given one a physical. Believe me, we had a lot of people call us, but in spite of what some people are saying out there that we are doing, that's simply not true," Belichick said.

The team's star was hit hard in the first quarter of Sunday's game against Kansas City when he was caught in the backfield by Chiefs safety Bernard Pollard.

"He was in a lot of pain," Pollard said. "When you hear a scream, you know that."

NFL officials reviewed the play and determined that 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.

Patriots players reacted with disappointment to the news.

"It's a shock, you know, when you lose anyone, especially a quarterback," lineman Richard Seymour said.

"We are disappointed. Tom was a tremendous leader on this team. He is a valuable member in this locker room, as well as a good friend of ours. We are very disappointed," Patriots safety Rodney Harrison said.

"You feel bad for Tom, and our thoughts are with Tom and whatever situation he is going to have to deal with," Patriots linebacker Mike Vrabel said. "Life goes on. There are a lot of games left. We won a lot of football games around here, and that is not going to change."

The Patriots have brought in a veteran quarterback Chris Simms, formerly of the Tampa Bay Buccaneers, who will be in town to at least undergo a physical if not to work out with the team.

Brady has won 78 percent of all his starts, the best record of any quarterback in the Super Bowl era. If his 14-3 playoff record is added in, his winning percentage jumps to 79 percent.

He's has also won three Super Bowls and he started his 128th straight game Sunday, the third best record of all time.

It was seven years ago this month that Brady, the backup quarterback for Drew Bledsoe, got his big chance after Bledsoe suffered a chest injury on the field in a game against the New York Jets.

Brady's injury is a nightmare to all die-hard New England fans, who have been waiting for an update. They also held their breaths Sunday as backup quarterback Matt Cassel replaced Brady on the field.

"They needed a starter, and you have to be ready to go," Cassel said. "We have to move forward. The game plan didn't really change or deviate from what it was with Tom in the game."

"I let him know that we have his back, and we're going to go out there and do the best we can for him to try and make plays and make his job as easy as possible. I think he did pretty good for a guy who you all thought should have been cut. I think he did an excellent job coming in and he did really well," wide receiver Wes Welker said.

Cassel failed to throw a single touchdown pass during pre-season play while Brady nursed a sore right foot, but he led the team 98 yards down the field to throw a touchdown pass to Randy Moss after Brady left the field.

"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 chinstrap and the guys rallied around me. I felt their support."

His performance left many fans optimistic about Cassel's abilities.

"Matt Cassel did great. He did awesome. Considering the pre-season, he came back and he just was very organized and knew what needed to get done, had a lot of focus and did the best," fan Margie Ahnell said.

The Patriots did go on to beat the Chiefs with a 17-10 win, the team's 20th straight regular season win, but with Brady hurt, most fans were in no mood to celebrate the victory.