Even though pro football revolves around the quarterback, it's hard to handle quarterback trades like auctions, particularly for quarterbacks in their mid-30s. McNabb is 33, not a bad age for a quarterback. He's still in his prime. Compared to Brett Favre, he's still a kid.
But the team that would ultimately trade for McNabb must be a only quarterback away from contending for a Super Bowl. The top teams have their quarterbacks, so finding the right trading partner is a little trickier than the Eagles expected, and that's why you have yet to see McNabb move to a new home.
The teams the Eagles targeted were the 49ers, Cardinals and Vikings. Minnesota didn't bite because it expects Favre to come back. The asking price of a first-round pick plus the $11 million-plus salary scared off the Cardinals enough that they made other moves, signing Derek Anderson. The 49ers signed David Carr. Unless both teams are willing to give up on their former No. 1 picks -- Matt Leinart in Arizona and Alex Smith in San Francisco -- those two NFC West teams can be scratched from the list.
History has shown that an aging quarterback with elite ability can add five to six points to an offense. Favre added 8.6 points to the Jets' offense in 2008 and 5.7 to the Vikings' offense last season. Steve McNair added 5.5 points a game to the Ravens' offense in 2006. A 37-year-old Jeff Garcia added 7.7 to the Tampa Bay Buccaneers' offense in 2007.
Favre turned the Vikings from a 10-win team to a 12-win team that went to a conference championship game. McNabb could have kept the Cardinals at the 10- to 11-win level and maybe taken the 49ers to the same, but the price was too high. Favre went to the Jets for a second-round pick. McNair went to the Ravens for a fourth. He was the same age as McNabb.
So why wouldn't other teams jump at the chance to add five to six points to their offense? The answer: expectations. To make a bold move on McNabb for a first- or second-round pick, the team making the trade must be thinking about going to a championship game, not just being a wild-card contender.
Which brings us to the Oakland Raiders, who have been buried in a four- to five-win funk seemingly forever. With JaMarcus Russell at the helm much of the season, the Raiders averaged only 12.3 points a game in 2009.
There is no doubt McNabb could make a major impact on the Raiders. He's a 60 percent thrower, so you figure he would add a lot of efficiency to the Raiders' offense. But the Raiders' offensive line has problems, so McNabb might be sacked 45 times instead of the 35 he had in Philadelphia last season.
Still, McNabb would give the Raiders about 231 net passing yards a game. Compared to the team's 159.8 yards a game last year, McNabb's presence should be worth three to maybe four more wins.
Unfortunately for Raiders fans, three to four wins may not make enough sense for the team to give up a second-round choice for a chance at an eight- or nine-win wild-card run. The move would not be similar to the Rich Gannon signing of 1999, because getting McNabb might not be a long-term solution. The Raiders signed Gannon when he was 33 to a four-year contract.
McNabb wouldn't want to sign a long-term deal with the Raiders. Sure, Davis could franchise McNabb in 2011 if there is a franchise tab, but McNabb wants to play only for the Eagles unless the Eagles find a trading partner that appeals to him.
Where the Eagles might have blown it is by letting the Cleveland Browns get away. Had the Eagles come to the Browns with an offer to give up McNabb for a third-rounder and maybe a conditional pick in 2011, Mike Holmgren and Tom Heckert might have been intrigued. The Browns instead signed an aging Jake Delhomme and traded for Seneca Wallace and are now out of the market. At the very least, keeping the Browns involved might have started a bidding war that could have netted the Eagles a second-rounder.
Back to the Raiders: Gannon did in his first year what McNabb could probably do, completing 19 of 32 passes a game. Still, the Raiders finished 8-8, but at least Davis knew he had three more years of Gannon. With Gannon, the Raiders became contenders until he retired.
Unlike Gannon, whose offense averaged 24 points a game in 1999, McNabb might be able to get only 20 points a game out of the current Raiders offense. Getting 20 points probably points to a seven- to nine-win season, not good enough for Davis to hand over a second-round choice.
The other history lesson the Eagles might not have studied is what happened to the Packers after trading Favre. Aaron Rodgers was a star sitting on the Packers' bench. I'm not sure Kevin Kolb can be as good as Rodgers, but let's say Kolb can be pretty good.
The Packers traded Favre out of the NFC to the AFC, not totally blocking a chance for Favre to return to the NFC North. In his first year as a starter, Kolb can expect to lose the close games like Rodgers, who threw for over 4,000 yards in 2008 as a first-time starter but couldn't prevent the Packers' win total from dropping from 13 to six. Under Kolb, the Eagles might drop a couple of games.
Favre ended up back in the NFC North with the Vikings, who have now won back-to-back division titles over the Packers. Let's say McNabb goes to the Raiders and leaves after a year. Where do you think he goes?
You got it. McNabb could end up with the Vikings in 2011 as Favre's replacement, and if Kolb becomes good enough to keep the Eagles playoff contenders, McNabb may have the edge over the Eagles if they meet in the 2011 playoffs.
History shows it's often better to ride your once-in-a-generation quarterback until he retires.
John Clayton, a recipient of the Pro Football Hall of Fame's McCann Award for distinguished reporting, is a senior writer for ESPN.com.