IF ONE MORE person tells me how doomed the Eagles are if Michael Vick goes down, I'm going to take a hammer to my Donovan McNabb bobblehead doll.

Maybe if we were in another town, or if we had changed the head coach, or even if we were in another era. But this is the land of Jeff Garcia, the land where there once was a raging debate over whether A.J. Feeley was better than McNabb when both were in their prime. The history of backup quarterbacks piloting your team into the playoffs is so rich - well, to steal the team owner's famous phrase, the Eagles truly are the gold standard in that regard.

Give the head coach that. There have been so many big performances by backups in the Andy Reid era that I had to look up some of the more forgotten ones. Koy Detmer and Mike Whatever-The-Hell his name was, for starters.

'Cause they were, like, better than McNabb.

For, like, a couple of weeks anyway.

This season does not rest solely on the shoulders of Vick. Lord, it was just two summers ago that knowledgeable folk around here - you know the ones who blabber endlessly about pocket passers and arm strength and three-step drops and West Coast offense and . . . well, anyway they were saying Kevin Kolb was a no-brainer, a superstar in the Kurt Warner mold.

Oh, well, all the blabber got us a nice defender in Dominique Rodgers-Cromartie. And that's the thing. 'Cause Vick was healthy at the start of last season and the Eagles had a whole bunch of leads heading into the fourth quarter and, well, you know what happened.

Michael didn't play any defense.

Few guys did.

The Eagles will be doomed if they can't get off the field on third down, as they again could not in Monday's preseason victory over the Patriots. They will be doomed if they get gorged again on big plays as they did last year, if they fail to tackle people as they did last year, if Juan Castillo is no more successful at the start of this season as it was at the start of the last one.

You want to worry about something, worry about that. Worry less about Vick and his health. Worry more that Reid has tied what could be a last stab at a Super Bowl to the acumen of a second-year defensive coordinator whose first unit has thus far showed few signs of curing last year's recurring ills.

Last year, it was Nnamdi Asomugha whose stock plummeted playing in Castillo's defense. Thus far this preseason, it's DeMeco Ryans who hasn't played up to expectations. And the rest of them? They still don't tackle well. They still too often seem tentative and confused out there.

To those who expressed stunned surprise at Andy Reid's sideline outburst Monday, I ask only this: Can you even imagine such a scene when Jim Johnson was his coordinator?

Now, so we're clear: I get it. It's less likely that the Eagles will reach the Super Bowl with either Mike Kafka or the latest flavor, Nick Foles, than with Vick. But at least concede they made the NFC semifinals with Garcia. At least concede that Super Bowls have been won with the likes of Jeff Hostetler, Mark Rypien, Trent Dilfer, Brad Johnson and Earl Morrall, and reached with the likes of Rex Grossman, Stan Humphries, Jake Delhomme, and David Woodley behind center.

Critics cite Vick's ability to extend plays with his feet as a reason he won't get there, or more specifically, as a reason he cannot stay healthy long enough to do so. But that's not how he gets injured. It just isn't. When he runs, he has the instincts of a running back, sees the hit coming, is able to avoid it. He gets injured because he too often holds the ball too long in the pocket and doesn't shuffle his way out of danger the way other guys who sometimes hold the ball too long do - Tom Brady and Dan Marino come to mind.

That's just not going to change. And if there's an over/under line in Vegas on how many games he will play this season, take the under.

But it's not the biggest reason the Eagles might be doomed from the start. Andy has proved he can overcome an injured quarterback. His reputation was enhanced during several of those seasons, in fact.

What he has yet to prove is that he can bring the defense back to the level it held under the late Jim Johnson. His hiring of Johnson in 1999 was a stroke of good fortune that has defined his success as a head coach like no other move he has made before or since.

His faith in Michael Vick might challenge his 14th season as Eagles coach, no doubt.

But it's his faith in Juan Castillo that might keep him from a 15th.

Contact Sam Donnellon at donnels@phillynews.com. Follow him on Twitter @samdonnellon. For recent columns, go to philly.com/SamDonnellon.