In general, a team’s brand-new head coach, especially a first-time head coach, needs to have all his key players in place when the games start. Not necessarily for the preseason opener, not in uniform or on the field, but it helps him to know who he can count on.

No such luck for the Eagles’ Doug Pederson, then. His debut Thursday night in Philadelphia against the Buccaneers makes him one of the first two new coaches to take the field this season. Coincidentally, the other is opposing coach Dirk Koetter. However, he has a problem Koetter doesn’t: The likely long absence of a crucial offensive player. Tackle Lane Johnson faces a 10-game performance-enhancing drug suspension, according to reports.

Suddenly, the preseason opener is more complicated, which is saying a lot for what Pederson already faced. He replaced Chip Kelly, he installed a new offensive system, the front office undid lots of Kelly’s moved and stirred up the roster and he’s already had to navigate a brief offseason quarterback clash involving Sam Bradford and the franchise’s future cornerstone, Carson Wentz.

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Now, barring complete exoneration of Johnson in his appeal, Pederson has to replace a vital component of his offense, for as many as 10 regular-season games, at a very vulnerable position — one that the Eagles drafted Johnson three years ago to solidify.

How vulnerable? Left tackle Jason Peters, who strained his quad last week, is one of the Eagles sitting out the opener. That’s nothing unusual or worrisome, and actually is par for the course across the league for the first preseason game. 

Still, Peters is 34 and was hurt much of last season … and Johnson, the starter on the right side, was drafted to be his eventual replacement (and, now, is paying him to be). Pederson had said earlier Tuesday — before the suspension report had gone public — that getting Johnson work on the left side was part of the training camp and preseason plan, even though, for now, he’s still on the right.

“Yeah, I think there would be a time to do that,’’ Pederson told reporters. “Like everything else, this would be the time to get him some work over there. So, that’s something that (offensive line coach Jeff Stoutland) and I will continue to talk about. I think (we would) definitely leave it open to be able to give him a few reps or at least a day over at the left side.”

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A possible second PED suspension in three years would make a mess of that plan for this season and add to the turmoil of trying to rebuild a line that was a mess in Kelly’s final, disastrous season last year.

The shake-ups at the skill posi

tions were going to be fascinating enough for the Eagles in the preseason. Bradford is the starter, but Wentz, the second overall pick, will make his NFL debut in the second half. 

DeMarco Murray is in Tennessee now, so Ryan Mathews takes the lead … and, as often is the case, was healing from another injury as camp opened. Wide receiver Jordan Matthews, still counted on to be the go-to receiver, is out with a bone bruise on his knee, but the Eagles are relieved it’s not as serious as originally feared.

The problem is everything else in Pederson’s offense could click right away, including the oft-injured, wildly-inconsistent Bradford. And it would all be moot because Johnson would be absent, and the domino effect would throw the entire line into chaos.

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“I’m thrilled — I am looking forward to it, and just can’t wait for Thursday,’’ Pederson said of his first game in charge.

But, again, he said that earlier in the day, while he thought Lane Johnson would be there for him.