Williams' absence wasn't surprising, given that he stayed away from the mandatory minicamp in June over issues with the organization's medical staff, multiple sources have told ESPN.
He had a growth removed from his head in the offseason, and those close to him have said he was upset with how many years it took for them to address the situation. But one Redskins source said the team made appointments for him over the years that he did not keep.
"I concentrate on the guys who are here right now," Gruden said. "We know how we feel about Trent, how important he is to this team. We expect him here shortly. Right now, there are some things he has to work out individually, personally, with his agent ... whatever that may be. Love Trent, love what he's done for this franchise and this team."
Gruden said he did not take it personally that his best lineman -- and arguably his best player -- did not report on time.
"It's the first day of training camp," Gruden said. "It's just something we have to go through. It's business at this point. I expect him to come back. Hope is not a word I'm going to use; I expect him to come back. He understands what this franchise has done for him and he understands what he's done for this franchise. Hopefully we get him back soon."
Williams has two years remaining on his contract, but the Redskins would save $12.75 million against the salary cap if they cut him this offseason. His career has been marked by excellence -- seven straight Pro Bowls -- and injuries. He hasn't played a full season since 2013.
In the last three years, Williams, a team captain, has missed a combined 13 games while playing hurt in numerous others.
It's uncertain whether the Redskins would attempt to assuage him by extending his contract or providing more guaranteed money over the next two seasons. Or if that would be enough to prompt his return.
Though Gruden and team president Bruce Allen had told reporters Tuesday they expected Williams to report, others with the team had privately expressed pessimism.
The Redskins could trade Williams, but that's a move they likely wouldn't strongly consider until just before the season, when they'd have a better idea on his willingness to return. While it might help the team down the road in terms of a high draft pick, it certainly wouldn't be best for Gruden, who has had three straight non-playoff seasons.
Christian struggled last summer, tore his MCL after just one game and missed offseason practices while rehabbing. Flowers, a former first-round pick, struggled at the position in four seasons with the Giants. The Redskins signed him to compete for the starting job at left guard, but without Williams and Christian this spring, Flowers had to spend almost all his time at tackle rather than at the position he still must learn.
The Redskins want to have a strong run game, so not having Williams would provide a major obstacle to that goal. They also have rookie quarterback Dwayne Haskins, a pocket passer who isn't expected to start immediately but will need protection when pressed into action.
Williams' teammates have been supportive of his actions.
"It's about time someone like that stands up," tackle Morgan Moses said this spring. "It's not just a situation here; it happens throughout the league. To have one of our peers like Trent to stand up like that means a lot. His scare is one you never want to have, but you've got to take care of yourself."