Coach Mike Zimmer called it a "significant knee injury," but added the Vikings "don't know the extent of it yet."
Zimmer said Bridgewater was sedated and undergoing an MRI.
He dropped back to pass during a drill, planted his foot and immediately went down. Trainers rushed to Bridgewater's side and began inflating an aircast, while the quarterback appeared to be holding his left leg.
Several players threw their helmets and shouted expletives as they scattered, and many simultaneously dropped to one knee in prayer. Moments later, a siren-blaring ambulance pulled into the team's Winter Park headquarters, stayed for about 10 minutes and then pulled away.
Bridgewater was still on the practice field grass as the team's public relations staff ushered reporters from the premises.
"Today is a disappointing day. ... The No. 1 thing is Teddy is such a great kid," Zimmer said. "Everyone loves him."
Players were visibly distraught as they exited the field.
"We're gonna grieve today and be upset about it," Zimmer told reporters.
Players from all over the NFL took to Twitter to show their support of Bridgewater.
If Bridgewater is unable to return in a timely manner, there is little behind him on the depth chart. Shaun Hill is the primary backup, but he's 36 years old and has played only sparingly over the past five years.
"I have confidence in Shaun, I think he's played great this preseason," Zimmer said. "The thing we all have to remember is this is about the team, we have a good team."
Bridgewater is entering his third season in the NFL and the Vikings were counting on him to take major steps forward after a promising start to his career. He helped lead the Vikings to the NFC North championship last season as more of a game manager, but Zimmer and offensive coordinator Norv Turner have said that they expected him to be much more of a playmaker in 2016.
Bridgewater missed the second preseason game with a sore shoulder, but was sharp on Sunday against San Diego. He went 12-for-16 for 161 yards and a touchdown in two quarters, leaving Vikings players and fans confident as the team starts to prepare for the season opener at Tennessee on Sept. 11.
The Vikings host the Los Angeles Rams in their final preseason game Thursday night, though Bridgewater and most of the starters were not expected to play.
Minnesota was a popular Super Bowl bet in Las Vegas. As of Sunday at the Westgate SuperBook, only the Green Bay Packers, Pittsburgh Steelers and New England Patriots had attracted more bets to win the Super Bowl than the Vikings.
The Westgate moved the Vikings' Super Bowl odds from 20-1 to 30-1 Tuesday afternoon, following news of Bridgewater's injury.
"Everybody can count us out but I think that'd be the wrong thing to do," Zimmer said.
The Associated Press contributed to this report.