Tom Brady went from the disappointment of a Super Bowl loss to the devastation of an injury that could keep him out for the rest of the season.

After missing the entire preseason with an unspecified foot injury, Brady left Sunday's season opener against the Kansas City Chiefs in the first quarter after being hit on the left leg by Chiefs safety Bernard Pollard. Coach Bill Belichick provided no information on the injury, but Pollard had a diagnosis of his own.

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

Various reports Sunday night said Belichick told the players that the injury was serious. The Patriots were already looking for a possible replacement for Brady. A person familiar with the situation told The Associated Press that former Tampa Bay quarterback Chris Simms was coming in today for a physical.

Brady was the NFL MVP last season after throwing for a record 50 touchdowns and leading the Patriots through a perfect regular 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.

Any chance at redemption might have disappeared when Brady, who has started 128 consecutive games, went to the turf clutching his left knee midway through the first quarter. After being tended to on the field, he walked off, limping, between two trainers.

Brady, 31, went to the locker room and wasn't seen again on the sideline as backup Matt Cassel led the Patriots to a 17-10 victory. The two-time Super Bowl MVP was not available for comment after the game, and Belichick said he had nothing to add to the in-game announcement that it was a knee injury.

"They're looking at him, doing some tests on him, so I don't have any information there," the coach said, cracking a smile as he added, "doubt anybody's interested."

The Chiefs also lost their starting quarterback when Brodie Croyle was sacked in the third quarter. The team said he had a bruised right shoulder, and he was replaced by Damon Huard.

Brady was 7-for-11 for 76 yards, completing a 26-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.

Another AFC quarterback suffered a knee injury on Sunday.

Vince Young was on crutches after spraining his left knee late in the Titans' 17-10 win over the Jacksonville Jaguars.

Tennessee coach Jeff Fisher said his quarterback will have tests to determine the severity of the injury, but added that Young's knee eased up in the locker room.