Williams underwent a procedure to remove a benign growth from his head this offseason, which apparently has led to some of his frustration. According to a source, some of Williams' desire also is to renegotiate his contract, which expires after the 2020 season.
Coach Jay Gruden said Williams wouldn't have been able to practice even if he had been at Redskins Park this week.
Williams, a seven-time Pro Bowler who hasn't played a full 16-game season since 2013 because of injuries, could feel this is his final chance to parlay any leverage into a new deal. The Redskins lack depth at tackle -- Ereck Flowers is working with the starters, for now -- and Williams is widely considered the team's best player.
However, because the 30-year-old is under contract, the Redskins don't have to do anything.
"Well, I know he's frustrated," Gruden said. "Any time you have something done, a procedure like that, of that magnitude, you want to find the reason. You wish something, maybe, could've been done differently or different timing, but our doctors are very good. I know they did the best they can. I mean, they have plenty of degrees. I know they did the right thing in their mind, and I know Trent's probably frustrated.
"But at the end of the day, we want him back, staff wants him back, players want him back and hopefully we'll get it fixed."
The Redskins have been one of the NFL teams hardest hit by injuries, having placed 52 players on injured reserve the past two years combined. There have been complaints by various Redskins players over the years regarding the medical staff -- often focusing on the lack of communication during recovery periods.
Redskins right tackle Morgan Moses said he was glad Williams is making a point. He referenced the business side, but also referred to the medical part of the game.
"It's about time someone like that stands up," Moses said. "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."
Gruden said he became aware sometime in the past week of Williams' displeasure and desire to skip the minicamp. There is a belief in the organization that he'd like a new contract as well, seeing how other players -- such as Antonio Brown and Le'Veon Bell -- have parlayed their situations into new deals.
Running back Adrian Peterson, a close friend who works out with Williams in Houston, said he doesn't know about any trade demands made by the nine-year veteran.
"I expect him to be back [for training camp]," Peterson said. "I don't see why that wouldn't be the case."