Suppose Bernard Pollard had missed Tom Brady's left knee on that sunny September day five years ago. Suppose those Hall of Fame-bound ligaments hadn't been snapped, leaving the league's flagship franchise in the hands of a 26-year-old kid who never had even started a game in college, let alone the NFL.

"I guess we'll never know," said Matt Cassel, that former kid and current Vikings backup quarterback. "But all I know is I was in my fourth year and he was Tom Brady, quarterback of the New England Patriots. No one else was going to step on that field unless it was a mop-up deal. But it turned out …"

Cassel paused. He has reached that moment in the conversation. The moment that's honest and innocent, yet still uncomfortable to say out loud for a backup at the one position in which starters play until they are seriously injured, woefully inept or insurmountably ahead.

"Unfortunately for Tom and fortunately for me," Cassel said, "things turned out well for me."

Had Pollard missed that knee? Well, let us count three possibilities:

• Brady probably would have finished that opening-day victory over the Kansas City Chiefs and completed the season. Why? Because that's what he has done every other year since 2001.

• Josh McDaniels might have remained a young Patriots assistant coach hidden in Brady's considerable shadow instead of becoming head coach of the Denver Broncos.

• And Jay Cutler might still be the quarterback in Denver. Why? Because McDaniels wouldn't have been forced to trade Cutler to Chicago after a failed effort to acquire Cassel, a nobody who never would have become a high-priced somebody had he not gone 10-5 in Brady's absence.

"I've been very blessed," Cassel said. "The part about me not starting [at Southern California] is probably the craziest part in all of this. To go from that to actually getting drafted [in the seventh round in 2005] and going to the best situation possible with the Patriots is being blessed. Being mentored by Tom Brady and then getting an opportunity, and then being ready for that opportunity, it's proof that you really are one play away from everything changing."

For the first time since 2008, Cassel enters a season as the designated No. 2 quarterback. But this time is different. This time, he wasn't drafted to fit a particular system. This time, he picked the interested party that best suited him. This time, he's backing up Christian Ponder, a third-year pro who has reached a career crossroad. Feel free to read between the lines.

Cassel will make $3.7 million — including a $2 million roster bonus and a base salary of $1.65 million — this season. That's a nice sum for a veteran backup, but not so hefty that it undermines the Vikings' steadfast argument that Ponder is their starter this season. Yes, Ponder will make less money ($1.3 million), but that's the result of operating under a rookie contract, not the team's judgment of his value compared with Cassel's.

Where things could get interesting is the second year of Cassel's contract, when either side can opt out of the deal without further salary cap ramifications. In other words, if Ponder's career solidifies, Cassel can choose to leave rather than stay on as a backup. If Ponder's career disintegrates, the Vikings could change starters relatively cheaply. Cassel would be paid $4 million and Ponder would receive his guaranteed $1.76 million salary for 2014.

"Christian has had his highs and his lows; he's been through the storms that other quarterbacks have been through," Vikings quarterbacks coach Craig Johnson said. "But this much I know: When the pressure was on last December and we had to have him step up, he played at a high level, we finished 4-0 and we made the playoffs. If Christian is playing at that level, then we're not even having this discussion [about contracts]."

Filling a need

Ironically, the Vikings didn't pursue a player capable of replacing an ineffective Ponder until they lost an effective Ponder to injury heading into last year's playoffs. But first, identifying that player went much deeper than arm strength and experience.

"I wanted that guy to know Christian is our starting quarterback," coach Leslie Frazier said. "I wanted him to know exactly what his role would be."

Cassel said all the right things in his interview with Frazier, Johnson and Vikings General Manager Rick Spielman. Of course, Cassel also needed a job, having been recently released by the Chiefs after a disastrous 2012 season.

"With Matt, I think some of it is just instinct from being around people and talking to people," Frazier said. "When I sat down with Matt, I trusted that the things I said to him were making sense and that he'd adhere to those things. Not just sign the contract and then come in here mouthing off, saying, 'I'm better than Christian Ponder, I should be this, I should be that.' "

Most important, Ponder seems comfortable with Cassel. He acknowledges that his leash got shorter, but doesn't sound worried that Cassel will try to undermine him with faulty advice or locker-room politicking.

"The first call I got when we were going to sign Matt was from Rick Spielman," Ponder said. "The second call I got was from Matt saying he was just coming in to help me and that he understands his role. And he's lived up to that. He's taken extra time to sit down with me and talk to me."

Johnson started coaching quarterbacks in 1989. He went down similar paths twice with the Tennessee Titans. The first came in 1999 when Neil O'Donnell, who had led the Steelers to the Super Bowl four years earlier, backed up an already-established Steve McNair. The second came seven years later when Kerry Collins, the fifth overall draft pick in 1995, began backing up rookie Vince Young, the third overall pick in 2006.

"You can have one of two mindsets when you come in as a veteran backup," Johnson said. "One, you can say, 'I'm going to do everything I can to win the job and I can care less about the starter.' The other mindset is, 'I'm a pro. I'm not going to disrupt the chemistry of the team, but I'm also going to be ready to go at a moment's notice.' Guys like Neil, Kerry and Matt, they're pros because that's how they wanted their backups to act when they were starters."

Whatever Ponder experiences this season, no doubt Cassel can tell him, as Johnson says, "been there, done that."

Success in his past

On a positive note, Cassel has won 10 games as both a backup in New England and a starter in Kansas City in 2010. He has made the Pro Bowl and led the Chiefs to their first AFC West title in seven years. In 2009, the Chiefs gave up the 34th overall draft pick for him and then signed him to a six-year, $62.7 million deal.

On the flip side, injuries and ineffectiveness have cost him 15 starts over the past two years. He was booed at a celebrity softball game and cheered last season when he suffered a head injury at home against the Ravens. Afterward, right tackle Eric Winston lashed out at Chiefs fans, calling their actions "100 percent sickening."

"I had a good time in Kansas City," Cassel said. "But a new start was exactly what me and my family needed. The fans have been great. It's refreshing."

Fans cheered when Cassel came on for an extended first-half look in Friday's preseason opener, a 27-13 loss to the Houston Texans at Mall of America Field. Ponder played only two snaps over 43 seconds, leaving after a poorly thrown pass was intercepted. Cassel played the rest of the half, completing 12 of 19 passes to eight receivers for 212 yards and one touchdown with one interception and a 96.8 passer rating.

Friday night had its highlights and lowlights. Cassel showed some veteran poise when he looked off a linebacker on a 56-yard pass to Stephen Burton and later sidestepped a blitzing linebacker and alertly found tight end John Carlson for a 10-yard gain to the Houston 2-yard line. But Cassel also was easily intercepted when he threw a weak pass across the field.

"It's never good to have those," he said. "But these games are learning experiences."

At 31, Cassel is not even sure he would still be having NFL learning experiences if Pollard had missed Brady's knee back in '08.

"I actually played with Bernard for a few months [during the 2009 preseason]," Cassel said. "He was a great guy. We got along. Naturally, everybody laughed about how he was the guy who, unfortunately for Tom, gave me my opportunity."