Tom Brady will miss the rest of the season, the New England Patriots said Monday.

"We feel badly for Tom about the injury," head coach Bill Belichick said during a news conference Monday. "You hate to see anyone go down. No one has worked harder or done more for this team than Tom has."

The Patriots quarterback left Sunday's season opener against Kansas City midway through the first quarter with a knee injury. The two-time Super Bowl MVP, who has started 128 consecutive games for the Patriots, was helped off the field after being hit by the Chiefs' Bernard Pollard.

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

Brady did not return to action. The quarterback had an MRI on Monday to determine the extent of his injuries. Belichick said during Monday's new conference he did not have many details on Brady's knee injury, but the team said he will under go surgery and will miss the rest of the season.

He will be placed on the team's injured reserve list.

Various media reports speculated that Brady tore his anterior cruciate ligament, but the team did not confirm the reports Monday.

With Brady out, the team's focus turns to who will take over for last year's MVP.

The Patriots were expected to bring in quarterback Chris Simms for a physical -- and possibly a workout -- Monday. ESPN reported the team is also looking at passer Tim Rattay.

However, Belichick said during Monday's news conference that the team has not yet decided who will play at quarterback for the rest of the year.

"We have not worked out a quarterback," Belichick said. "We've had a lot of people call us, I can tell you that."

In the meantime, backup Matt Cassel is expected to take over under center when the Patriots face Brett Favre and the New York Jets next week. After taking over for Brady in the first half of Sunday's season opener, Cassel led the team to a 17-10 victory over Kansas City.

"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 preseason, 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 told Boston television station WCVB.