New England quarterback Matt Cassel is on target to command top dollar in the NFL free-agent market during the offseason.

The Providence Journal / Bob Breidenbach

FOXBORO — On Sept. 6, where Matt Cassel played in the 2009 season wasn’t much of a hot topic.

The fourth-year backup quarterback hadn’t been on the field much, and it was conceivable that he would re-sign with the Patriots, continuing as the team’s second-string signal-caller.

But then Sept. 7 came, and in the weeks that have followed, Cassel has gone from relative unknown to hot commodity, someone who will likely garner a tidy sum on the free- agent market, particularly given the dearth of solid quarterbacks in the NFL.

So if New England doesn’t advance to the postseason, Sunday’s game in Buffalo will likely be Cassel’s last in a Patriots uniform. He was asked about that prospect yesterday.

“I don’t know. Nobody knows the future. If anybody knew the future, I probably wouldn’t be here right now because a lot of people predicted I wouldn’t be here after preseason,” Cassel said. “The fact is nobody knows where I’m going to be next year, so I could definitely be back here. It’s something we’ll have to wait and see.”

If Cassel is back next season, it would likely be at one heck of a discount — with Tom Brady’s salary cap number at $12.8 million next year, it’s not fiscally wise to have a backup who earns much more than the league minimum.

According to reports, Cassel should be able to garner a deal on the free-agent market that pays him anywhere from $6 to $10 million a season, with a chunk of that money guaranteed. That’s hard to walk away from, as is the chance to continue to be a starter.

While in some ways it seems crazy that a quarterback with 15 starts could command that sort of money, consider that the Oakland Raiders signed 2007 No. 1 draft pick JaMarcus Russell to a six-year, $61-million contract with just over half of that guaranteed, and he had never played a down in the NFL.

Among Cassel’s contemporaries, Green Bay backup Aaron Rodgers, who had not made a start before this season because he played behind iron man Brett Favre, received a six-year, $65- million extension in October. About $20 million of that is guaranteed.

In the final year of his rookie contract, Cassel is making $520,000 in base salary this season.

Yesterday, Cassel said he would like the chance to stay with the Patriots.

“I love this organization. I don’t know what the situation might be, but the Patriots are home to me right now. That’s all I’ve ever known in my professional career,” he said.

As he himself alluded to, it’s quite a change of field for the 26-year-old California native. With training camp winding down, and with him having looked shaky during camp, more than a few media members (including this reporter) had Cassel not making the Pats’ 53-man roster.

New England had Matt Gutierrez, who spent last season on the roster, and had drafted Kevin O’Connell in the third round in April; Cassel, it was believed, would be the odd man out.

The Patriots coaching staff clearly disagreed, and Cassel has rewarded its belief in him, completing 63 percent of his passes thus far for 3,615 yards, 21 touchdowns and 11 interceptions. His quarterback rating of 89.1 is respectable, and he’s fifth in the league when it comes to third-down rating (98.5).

Asked about those who may have doubted his ability to be a viable starter, Cassel seemed amused.

“I think it’s great. When you look back at the situation and you look at the naysayers and all the critics, it’s great to overcome those obstacles and let people know that you never know what’s going to happen in sports,” he said. “That’s the great thing about sports and especially the game of football. For me, it’s just a constant reminder to keep going out, working hard, be diligent about what you do and good things will happen.”

smanza@projo.com