FOXBORO — Sunday afternoon, the wrong Southern California quarterback will be holding the clipboard at Gillette Stadium.
The top draft pick with the Heisman Trophy, the $51 million contract and the jetsetting lifestyle most likely won't throw a pass as the Arizona Cardinals make their first trip here since 1994.
While on the other sidelines, Leinart's former backup at USC will continue to pen his improbable story for the Patriots.
Sunday, Arizona's Matt Leinart will earn $531,200 to watch his college pal, New England's Matt Cassel, take on the NFC West champion Cardinals. Cassel, by the way, will make $533,500 ... for the season!
How did this happen?
"I've overcome a lot of adversity," said Cassel, who in 2003 was beaten out by the redshirt freshman Leinart in a battle USC coach Pete Carroll has said was decided by the narrowest of margins. "It's taught me to keep pushing forward and keep moving on."
Leinart, who replaced Carson Palmer at USC, could heed his friend's approach to life on the sidelines. It wasn't supposed to be this way for the MVP of the 2005 Rose Bowl and 2006 Orange Bowl.
After a quick start ... Leinart made 11 starts as a rookie, including a 405-yard passing game against Minnesota ... nothing has come easily.
The Cardinals' original plan had been for the veteran Kurt Warner to ease the transition for Leinart to the pros, teach him the ropes then go out gracefully.
Instead, the two found themselves sharing time last year until a broken collarbone Leinart's sophomore season in October.
Since then, it's been all Warner, as Leinart, who was supposed to start this year, struggled in the preseason.
For a guy like Leinart, who ran with the Hollywood crowd at USC and looked destined for superstardom, it has been a culture shock. And then came the off-field problems, Internet photos of Leinart in a hot tub with a beer funnel and underage girls.
"I've taken some hits and I've learned from my mistakes and I've learned from everything I've been through," Leinart told SI.com back in training camp. "It's difficult. It's one of those things where I've come to realize that my life is magnified through the media in whatever I do. I just try to understand that but also realize that this is my life and I'm going to try to have fun."
Standing and watching is not fun, especially when it's your job. It took a special mindset for Cassel to be ready when Tom Brady's left knee was decimated back in September. He, after all, hadn't started since high school in 1999.
"As a backup quarterback, as a competitor, anytime, you want to be out there," said Cassel. "You want to be playing, so that part is very difficult. When you're able to step back and learn from a guy like Kurt, because he's so good and because he's so established, you can learn a lot of things."
Warner's play — he'll start for the NFC in the Pro Bowl — and the fact that the Cardinals have clinched their division, have allowed the 25-year-old Leinart to quietly play the understudy role.
To his credit, Leinart has reached out, to Warner and even to Cassel.
"We've talked (about it) back and forth throughout the season," said Cassel.
Meanwhile, Tom Brady's ex-backup motors along, earning the respect from around the nation that Leinart is still seeking.
"(Cassel) has always been a capable player," Leinart told the East Valley Tribune of Mesa, Ariz.. "He's a really good athlete, with a big arm. He can move. And he's smart. It's not really a surprise that he's doing what he's doing ... He's playing great. He's going to basically get that team to the playoffs."
Cassel has waited but he'll finally leap into Leinart's tax bracket, either by picking up $12 or $13 million next year as the Pats' "franchise player" or by picking up a multi-year deal elsewhere in free agency.
And he's confident that when the 37-year-old Warner is finally done, the Cards' high-powered offense will then be in capable hands.
"When Matt is ready to go and he steps in to take over that team, he'll be ready and more prepared than he was," said Cassel.
Until then, things will remain upside down, at least from where they were a year ago and from where most NFL experts expected they'd be.
Cassel offered Leinart one final bit of advice.
"Don't listen to people who are negative and work against you," he said. "Continue to surround yourself with people that are positive and can help you and things will turn around for you."