Tom Brady limped off the field in pain, and the New England Patriots can only hope their Super Bowl hopes didn't go with him.

The NFL's reigning MVP left Sunday's 17-10 victory over Kansas City midway through the first quarter with an injured left knee after being hit on a throw. There was no immediate word on the extent of Brady's injury — "I am not sure what we are dealing with," coach Bill Belichick said — or how long he would be out.

"It kind of looked bad," wide receiver Randy Moss said.

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 Monday for a physical.

Brady went to the locker room and wasn't seen again as backup Matt Cassel led the Patriots to the victory. Cassel, who had thrown just 39 passes in his first three seasons, could see a lot more action if Brady is sidelined next week — or beyond.

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

The 31-year-old Brady, who last season led the Patriots to an undefeated regular season and their fourth Super Bowl in eight years, wasn't available for comment after the game.

"He's the face of the New England Patriots, and Tom being who he is, it kind of hurts, to be honest with you," said Moss, who caught a record 23 TD passes from Brady last season.

On Monday night, Minnesota is at Green Bay and Denver is at Oakland.

At Foxborough, Mass., 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.

After missing the entire preseason with an unspecified foot injury, Brady was hit on the left leg by Chiefs safety Bernard Pollard.

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

Cassel went 13-for-18 for 152 yards and one touchdown.

"This is something I've been preparing for (for) a long time. It's not something that we expected to come up on opening day," Cassel said. "Since I've been here and been around Tom, he's always popped back up."

The Titans also aren't sure if they'll be without their quarterback for any time. Vince Young was on crutches at Nashville after spraining his left knee late in their win.Tennessee coach Jeff Fisher said his quarterback will have tests to determine the severity of the injury, but added that Young's knee appeared to ease up in the locker room.The Titans sacked David Garrard seven times and Cortland Finnegan intercepted him twice.

At Miami, Brett Favre made a successful debut, throwing for two touchdowns six months after calling it a career in Green Bay before changing his mind.Favre's new start with the Jets had a happy ending thanks to two late stands by New York's defense. Dwight Lowery batted away a fourth-down pass in the end zone with 9 minutes left, and Darrelle Revis intercepted Chad Pennington — again in the end zone — with 5 seconds left.Favre finished 15-for-22 for 194 yards and his 161st victory, extending his NFL record for starting quarterbacks.Pennington, the man Favre replaced, was 26-for-43 for 251 yards and two TDs for Miami.

Panthers quarterback Jake Delhomme threw a 14-yard touchdown pass to Dante Rosario as time expired in San Diego, capping a desperation drive for the win.Cowboys 28, Browns 10Terrell Owens caught a 35-yard touchdown pass, Tony Romo picked apart Cleveland's secondary, and Marion Barber scored on a pair of 1-yard runs for the Cowboys.

Matt Forte ran for 123 yards and one touchdown in his NFL debut, and Kyle Orton committed no turnovers to help Chicago beat Indianapolis in the first regular-season game at Lucas Oil Stadium.Two-time league MVP Peyton Manning didn't look like himself in his first game since having surgery to remove an infected bursa sac from his left knee in July. He went 30-of-49 for 257 yards with one TD.

At San Francisco, Kurt Warner passed for 197 yards and led three monotonously effective drives in the second half for Arizona..

Donovan McNabb threw for 361 yards and three touchdowns, and rookie DeSean Jackson had an impressive debut at Philadelphia.

At New Orleans, Drew Brees passed for 343 yards and three touchdowns, giving fans already jubilant about the Saints' quick return from Hurricane Gustav a triumph to celebrate as well.

Matt Ryan threw for a touchdown on his first NFL pass, and Michael Turner set a team rushing record with 220 yards and two TDs in his Atlanta debut.

At Orchard Park, N.Y., Roscoe Parrish scored on a 63-yard punt return, and punter Brian Moorman completed a 19-yard touchdown pass to defensive end Ryan Denney on a fake field goal.

At Baltimore, the Ravens forced two turnovers and limited the Bengals to 154 yards to make John Harbaugh a winner in his debut as an NFL coach.Cincinnati's Carson Palmer was 10-for-25 for 99 yards, and his interception ended the Bengals' deepest foray into Baltimore territory.