Panthers coach Ron Rivera said after Thursday's practice the move was made so the team to could focus on developing its young guards -- particularly Williams and rookie Edmund Kugbila.
The move was a bit surprising considering Hangartner had been running with the first team at camp, and Kugbila, the player Carolina drafted to eventually replace him, has missed the majority of training camp with a pulled hamstring after sitting out OTAs with a knee injury.
But Rivera said the team really likes Williams, who started nine games last year at right guard after a season-ending injury to Pro Bowl centre Ryan Kalil prompted the team to shift Hangartner to centre.
Williams ran with the first team on Thursday, while Kugbila remained out of action.
"We have Kugbila who is in the wings and Garry Williams who has done a really nice job and has had a nice spring in OTAs," Rivera said. "We're excited about what Garry can bring to the table."
Rivera said the Panthers had planned on Williams being their starting guard in 2011 before he broke his ankle in the preseason and was sidelined for the season.
"He seems to be back in shape playing the way he did when we thought he could be a starting guard," Rivera said of Williams, who has started 20 games in four seasons.
Rivera said the team has no plans to bring in a veteran free agent guard from outside the organization to compete for a starting job.
"We have a young group of guards that is pretty exciting," Rivera said.
Hangartner started 83 games during his eight-year career with the Panthers and Buffalo Bills.
Backup quarterback Derek Anderson called Hangartner one of the most popular players in the locker room, saying, "It's tough, but somebody is going to have to step up."
Hangartner was due to make $1.575 million this year.
Left tackle Jordan Gross, who has played six seasons with Hangartner, said he was surprised and saddened by the move.
"He got a text to go see coach Rivera first thing in the morning, and that's never good news," Gross said. "Honestly, I was wondering if he was going to get traded to Denver, because everyone knows they have a (injury) situation there. But yes, it surprised me."
Teammates often referred to Hangartner by his nickname, "Piggy."
Gross said the move is a solemn reminder that the NFL is a business.
"You hope that management knows what they're doing and that it is for the better and it will make us a better team," Gross said. "That's really what we have to focus on."
NOTES: Gross, the team's 33-year old, two-time Pro Bowl tackle, said Thursday he doesn't want to play for any other team except the Panthers, but said he isn't thinking about retirement. His contract was restructured this off-season in a manner that the Panthers will almost certainly have to release him after this season. But Gross reiterated he wouldn't rule out coming back to play next season for Carolina under a different contract "if they want me back."