No one on the Giants knows more about what backup quarterback Matt Cassel is capable of than Brandon Meriweather.

The veteran safety was on the 2008 Patriots when Tom Brady suffered a Week 1 knee injury and Cassel had to step into the starter's role. The Patriots went 11-5 that season.

"Matt was an athlete," Meriweather said. "He was a good runner and he had a strong arm. When he got his time to shine, he capitalized on it. He was that one player that if anything happened to Tom could go in there and step up."

Now he's not stepping in for Tom, he's stepping in for Tony.

The Cowboys have been without Tony Romo since Week 2, when he broke his left collarbone, and will be without him for the next month. Brandon Weeden started three games at quarterback for the Cowboys, but they were 0-3 in that stretch. So during the bye last week, Cowboys coach Jason Garrett named Cassel as the starter. He'll get his first start for the Cowboys -- and first actual start since Week 3 with the Vikings last season -- against the Giants on Sunday.

"Quarterback is a tricky position in that you evaluate how the player executes what you're asking him to do, but then you also have to evaluate how the offense does as a whole, and how the team does as a whole," Garrett said of the decision. "It's probably different from any other position that you have on your football team in that regard.

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"Brandon, for three starts for us, really did a lot of good things. But when we evaluated those three parts of it, how he played, how our offense as a whole played and how our team has played, we just felt like it was the best thing for our team going forward to give Matt Cassel a chance to be our starter."

Cassel has bounced around since those New England days. He spent time with the Chiefs and Vikings and competed for a job with the Bills this past summer. Technically he was the Bills' starting quarterback in Week 1 this year, lining up there for the first snap while Tyrod Taylor was split wide in a Wildcat formation. But he left after the one play and Taylor took over.

Now Taylor is hurt. Cassel likely would be stepping into the starting role for the Bills had he not been traded to the Cowboys after Romo's injury.

Cassel said he was coming off the practice field with the Bills when he got a text from his agent telling him he might be traded to Dallas. His first concern was for his wife, Lauren, he said, who was 36 weeks pregnant at the time.

"I was excited," Cassel said of the deal, "but at the same time, there were a lot of moving pieces with my family and everything else going on."

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It all worked out for the trade, for Cassel and for his wife and fourth child, who was born last week. Cassel was there for the birth because his new team was in its bye week, and he's been able to be around his family after practices since. Had he not been traded?

"I was supposed to be on a plane to go to London with the Bills [this week]," he said.

Instead of being in England, he's starting for America's Team.

"You never know in this league," he said when asked if he thought he'd ever start again. "It's the most unpredictable league to be in because of the physicality [and injuries]. I never counted myself out and I was always hopeful . . . You always shoot and your main goal is always to be out there on Sundays and playing and being a starter. I'm happy about the opportunity."

It's forced the Giants to do some extra studying. The last time they faced Cassel was on Oct. 4, 2009, when he started for the Chiefs.

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Some individuals have had glimpses of him along the way. Running backs coach Craig Johnson was Cassell's quarterbacks coach in Minnesota. After going 10-5 as New England's quarterback in 2008, his record as a starter since is 24-33.

The Giants have been looking at old video of Cassel to try to figure out how he'll fit in with the Cowboys' offense. Their best bet?

"I don't think that changes what they do," Tom Coughlin said. "Listen, without Romo and without [Dez] Bryant, they're averaging 350 yards a game. It's consistent."

Meriweather expects to see the same Cowboys offense he saw when they were at full strength in the opener against the Giants.

"I would assume that they're going to run their same stuff," he said. "Dallas has their great offensive line. I think you put it on their offensive line and you say, 'Win the game.' "

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So why the change at quarterback then? "Cassel is Cassel," Meriweather said. "I don't think people change too much. I think if you have one great season, then it's in you."