ASHBURN, Va. -- The Trent Williams holdout doesn't appear closer to a resolution. Or, perhaps, one could come tomorrow if: One side budges; another team makes a strong offer. It's at a stalemate; it remains fluid.

As the Washington Redskins prepare for Sunday's season opener at Philadelphia, their seven-time Pro Bowl left tackle remains elsewhere.

Here's a primer on the situation:

Why is Williams holding out?

Sources close to Williams say it's about the medical staff -- but that doesn't necessarily mean Redskins trainer Larry Hess and his staff. Some people close to Williams said it stemmed from how a growth on his scalp was diagnosed and handled over the years. He needed surgery to remove the growth this offseason. However, neither Williams nor his agent has commented publicly -- or said a whole lot privately.

Williams -- with a desire for security -- also has asked for more money but the Redskins haven't met any financial demands.

Will the Redskins extend his contract?

Williams, 31, has two years remaining on a five-year deal worth up to $68 million. His base salary of $12.5 million in 2020 not guaranteed. To extend Williams' deal would mean to make him the highest-paid tackle.

The problem here, again, is precedent. Linebacker Ryan Kerrigan also has two years left on his contract; the Redskins know he would want a similar extension. The same would be true of tackle Morgan Moses in 2020, when he has two years left on his deal. No team wants to get into a habit of extending too many older players. Giving Williams more guaranteed money in his final year would be another option, but it's uncertain if he would settle for that.

Who has the leverage?

The Redskins control Williams' rights so ultimately they have control. If he wants to sit out all season, they don't have to do anything -- and his contract would still have two more years. But Williams has leverage in this sense: The left side of Washington's line could be a big problem, one he could resolve. And the Redskins have a head coach in a must-win season.

Would the Redskins trade him?

Team president Bruce Allen told NBC4 Washington that Williams would play for the Redskins or no one. Coach Jay Gruden said he seriously doubts the Redskins would trade him and still feels "very strongly" about that opinion. However, Williams has told numerous people he won't play again for Washington. If that's the case, at some point the Redskins will have no choice and will make a move for the betterment of the franchise rather than try to win a battle with Williams.

So while the Redskins are proclaiming a hard line, a trade remains a definite possibility. However, they don't feel they have to trade him for any price.

What happens if Williams doesn't report?

He'll start missing game checks. With a base salary of $10.85 million, he'd collect $638,235 per week -- in addition to roster bonuses worth $15,625 per week. If Williams can withstand not collecting that cash, he could sit out a while. The Redskins fined him $40,000 per day through the preseason for not reporting, an amount they might not waive if he does report. Why? Once more: precedent. If they imposed this sort of fine in the future, players wouldn't take it as seriously.

How does the Laremy Tunsil trade to Houston affect this situation?

It removes one possible landing spot, though it's not certain Houston was interested in Williams. It's also hard to compare the situations. For starters, one view is that Houston gave away too much -- two first-round picks and a second-rounder -- in part because it lacks a general manager. One league source said only a coach, who might need to win sooner rather than later, would give away that much for Tunsil.

But Tunsil is 25, six years younger than Williams. While Williams would be considered better by most, that doesn't make him a better long-term investment. Tunsil, entering his fourth season, missed a combined four games his first three seasons. Williams last played in all 16 games in 2013, and he's missed a combined 13 games the past three seasons. He's also been suspended twice for violating the NFL's substance abuse policy.

What are the key dates to know?

The NFL trade deadline is Oct. 29. But Washington will need some team in the midst of a good season to have a desperate need at tackle. Then, perhaps, the Redskins could coax a first-round pick in return.

Otherwise, the next key week starts Nov. 18. In order for Williams to have an accrued season, he must be on the roster for six or more games; on that date, Washington will have six games remaining. If Williams is on the roster for fewer than six games, his contract would roll over. If Williams still has two more years left on his contract, he'd be easier to trade in the offseason. If the Redskins don't get a strong offer before the deadline, and if Williams doesn't report, this could be Washington's best option. The Redskins likely would receive only a draft pick in return regardless of when they trade, so there's no rush. They'd have a better chance to shop Williams once teams see what the draft might hold.