"Our thoughts are with him and his family during this time," coach Bill Belichick said before practice. "Right now we're just taking it day to day. He's going to take care of what he has to do."
Belichick said that Greg Cassel died Monday night and Matt has left the team to be with his family in Southern California. Belichick said he didn't know when Cassel would rejoin the team or whether he would be able to start Sunday against the Oakland Raiders.
The Patriots are practicing this week in San Jose. They stayed on the West Coast after last Sunday's 24-21 win in Seattle.
Cassel's teammates expressed their condolences for his loss and offered whatever support they could.
"It's a part of life," defensive lineman Richard Seymour said. "It's one thing that will happen to all of us someday. It's a tough situation. I don't think you're ever prepared for it. We support him and his family."
Matt Cassel is from Northridge in the Los Angeles area and his father and mother Barbara divorced when he was 14. Greg Cassel was a script writer.
Belichick had to go through the difficulty of the death of his father, Steve, during the 2005 season.
"It's bigger than football," Belichick said. "I've been through that during the season as well, a personal situation you just have to deal with, and as I said, our thoughts and prayers are with him."
Cassel has completed 64 percent of his passes since taking over for the injured Tom Brady in the season opener. He has thrown for 3,052 yards, with 14 touchdowns and 10 interceptions, looking better and better as the season has progressed.
If Cassel was unable to start this week, the Patriots (8-5) would likely have to turn to rookie Kevin O'Connell, a third-round pick out of San Diego State with four career passes.
O'Connell played briefly at the end of a blowout loss in Miami in September, completing three of four passes for 25 yards in the 38-13 defeat. The only other quarterback on the roster is Matt Gutierrez, who threw his only career pass as a rookie last season.
"Kevin learns every week," Belichick said. "He's a smart guy. Football is important to him he works hard at it and I think he gets better on a daily basis. He's getting better through the course of the year in the opportunities that he's had, which have been limited. But he's always ready to go when we put him in there.
Even though the Patriots are playing the struggling Raiders (3-10), they can ill afford a slip-up because of the tight AFC East race. New England is locked in a three-way tie with Miami and the New York Jets with three games to go.
The Patriots have remained in contention despite Brady's injury and believe that O'Connell could step in if need be.
"I haven't really seen much on him as far as game-time situations," defensive back Ellis Hobbs said. "We'll find out together. In practice he definitely has a strong arm on him, can throw the deep ball, can throw the intermediate routes. Just like any quarterback we have, they're great in the system. They can go and just put the ball wherever we need and let our skilled players do the rest."
DT Vince Wilfork and DE Ty Warren were both limited in practice. Wilfork left Sunday's game in Seattle with a shoulder injury. Warren was inactive against the Seahawks because of a groin injury. ... LB Tedy Bruschi is out with an injured knee that reportedly will sideline him for the remainder of the season.