Cable said he spoke with Seymour earlier this week and that the five-time Pro Bowl defensive end told him he wants to play for the Raiders, who acquired him from the Patriots on Sunday in exchange for a 2011 first-round draft pick.
Cable reiterated that he is hopeful Seymour will play for the Raiders but declined to discuss reports that the two sides were discussing a new contract. Seymour is entering the last year of a four-year, $30 million contract that he signed with the Patriots before the 2006 season.
"I don't want to comment about anything of that until we have something that's done and concrete," Cable said.
"Because we don't have rights to Richard, there really isn't anything I can say about him or his situation," Belichick said. "So I'll have to pass on those questions at this time."
Belichick refused to say whether the trade had been completed in the wake of Seymour's failure to report to the Raiders. Asked if the deal was done, Belichick noted that the Patriots no longer had the rights to Seymour and said the status of the trade was "not a topic that I'm going to address."
The NFL wouldn't talk about the trade either, although the move was included on the league's official transactions list and Seymour is listed on the Raiders' roster on their Web site.
"Any comment at this time would have to come from the teams," league spokesman Greg Aiello said.
Seymour was selected by the Patriots with the No. 6 overall draft pick in 2001 and began a string of five consecutive Pro Bowl appearances in the 2002 season. He played key roles on three Super Bowl-winning teams.
Seymour is the fourth defensive leader to leave the Patriots since last season after linebacker Mike Vrabel was traded to the Kansas City Chiefs and linebacker Tedy Bruschi and safety Rodney Harrison retired. Now younger players such as linebacker Jerod Mayo and defensive linemen Vince Wilfork and Ty Warren might have to fill leadership roles.
"We have a lot of good leaders on our team and especially on the defensive side of the ball," Belichick said. "No doubt about it, it's different, but I think it's good."
Patriots director of player personnel Nick Caserio said in a conference call that he had no comment on whether money saved from Seymour, who's scheduled to make $3.7 million in 2009, would help in negotiating with Wilfork, who's also in the last year of his contract and wants an extension.
Patriots defensive coordinator Dean Pees wouldn't talk about whether Belichick had asked for his input on the trade, which came one week before the team's Monday night season opener against the AFC East rival Buffalo Bills.
"This is not going to be an interview about Richard," Pees said in a conference call. "It's really about Buffalo and whoever we have here (to face the Bills)."
Belichick wouldn't say if the Patriots will be better without Seymour.
"We'll find that out starting this week," he said.
The Associated Press contributed to this report.