The cause of death of Greg Cassel, a noted script writer, was not disclosed.
Coach Bill Belichick said Matt Cassel's return is "day-by-day."
The Patriots face the Raiders in Oakland Sunday, and are preparing in San Jose after their 24-21 win at Seattle last weekend.
"From a football standpoint, we'll just handle it like we normally do," Belichick told reporters following Wednesday's practice. "Right now, we''re just taking it day-to-day. He's going to take care of what he has to do."
Matt Cassel, a Southern California graduate, is the NFL's ninth-rated passer, having completed 283-of-442 throws for 3,052 yards with 14 touchdowns and 10 interceptions.
If he does return for Sunday's contest, his likely replacement will be Kevin O'Connell, a rookie from San Diego State.