SAN DIEGO - The future of the Eagles offense is here, whether you (or they) are ready or not.

Sometime in the third quarter, Brian Westbrook left the game with his second concussion in three weeks. It is fair to wonder whether he should have been playing at all. It is also fair to wonder whether he will, or should, play again this season. Or ever, for that matter.

"We have to understand what's at stake," quarterback Donovan McNabb said. "The head is something you just don't play with."

If the Eagles truly did take every precaution before allowing Westbrook to return to action 21 days after being knocked cold at Washington, then they will have to err on the side of extreme caution now. Westbrook should be placed on injured reserve, ending his season.

That will leave McNabb alone among the kids who embody the Eagles' hopes even as their growing pains lead to afternoons like yesterday.

"Veteran leadership is something that we don't have that much of," McNabb said. "For the guys that are out there, we're trying to get the young guys going a little bit. But the young guys have to step up at this time."

With Westbrook in the starting lineup, rookie running back LeSean McCoy was barely seen at all. That tells you coach Andy Reid would prefer to ease McCoy into the offense. When he whiffed on a blitz late in the third quarter, resulting in a sack of McNabb, it was easy to understand why.

Reid has always resisted playing rookies, especially on offense. Now he has to rely on McCoy, Jeremy Maclin and second-year wide receiver DeSean Jackson for much of his offensive production. It's a high wire and McNabb is the guy forced to walk it.

And yet: 450 passing yards, 23 points that really should have been 30-plus. The offense looked stunning at times, darned near unstoppable until it stopped itself.

Those red zone follies weren't all about the young players. The veteran head coach has to take some of the heat for the way some very good drives fizzled.

First-and-goal at the Chargers' 1-yard line has to produce more than a field goal. It just has to, especially when the Eagles were trailing 14-0 on the road.

Reid had fullback Leonard Weaver run up the middle on first down. No gain. McNabb faked a handoff, rolled to his left and overthrew tight end Brent Celek on second down.

Then, in one of his smarter-than-the-average-bear moves, Reid sent Eldra Buckley into the game on third and 1. Buckley had not touched the ball up until that point. Not in the game, barely at all during the entire season.

"We've been working him in during the week down there in short-yardage and goal-line situations," Reid said. "That was his play. He'll pound it up in there and I thought we needed that right there. He'll hit it. That's what I know."

Buckley didn't hit it. At the time, I thought Reid should have gone for the touchdown on fourth down. If he had, and if the Eagles had been successful, it would have been a huge momentum boost.

"There was too much time," Reid said. "I thought it was important to come out of there with points."

As it played out, he was probably right. The Eagles were able to make it a game in the fourth quarter and those early field goals were necessary.

But that doesn't explain getting three cracks from the 1-yard line and never getting the ball to Westbrook, McCoy, Jackson, Maclin, or Jason Avant. The Eagles' inability to utilize their receiver with the most size and best hands remains a mystery.

Avant's 56-yard catch-and-run set up the Eagles' most painful red zone stumble. First and 10 at the 16 turned to third and 1 at the 7. With no apparent ability to pick up a yard with their running game, the Eagles ran a play designed to score a touchdown. Except McNabb heard defensive players calling out the play as the Eagles got into formation. The Chargers adjusted their coverage, pressured McNabb, and he ended up throwing the ball out of the end zone to avoid a sack.

Another chip-shot field goal and it was 21-9, Chargers. Three scores each, but it was not a close game.

"You just can't play games like this," McNabb said. "Mistakes, penalties, starting late. Once we got going, it was just too late. We need to find an answer quickly."

McNabb and Reid both seemed encouraged by what the offense was able to do, even as both acknowledged the team had let another winnable game get away. At 5-4, the Eagles are just a mediocre football team right now.

There is real promise in those young players. They are the Eagles' future. With Westbrook possibly done, for the season or longer, they're also the present. Ready or not.

Contact columnist Phil Sheridan at 215-854-2844 or psheridan@phillynews.com. Read his recent work at http://go.philly.com/philsheridan.