Foxworth tore the ACL in his right knee Thursday during an orientation practice.
"I was just running and tried to change directions, something I've done a million times in my career. This time it just didn't work," Foxworth said Friday. "It wasn't anything odd. It happened on grass, so I can't even blame it on turf."
Coach John Harbaugh said, "It's unfortunate. He wasn't touched. Nobody's worked harder during the offseason and we were counting on him."
Foxworth had four interceptions last season. He started all 16 games and both of Baltimore's playoff games.
After Baltimore's first full-squad workout of the summer Friday, Harbaugh told the players that the Ravens would have to move on without Foxworth.
"I can't wait to see who steps up. I can't wait to see who that we're all talking about a month from now that stepped up to fill that spot," Harbaugh said.
Foxworth, a five-year veteran, said he couldn't remember having an injury more severe than an ankle sprain.
"I just feel like I'm letting everyone down," he said. "I know it's stupid. Everyone keeps saying you didn't do it on purpose, obviously, but you're expecting to be there to help the team — and then you're not."
Even though Foxworth won't be covering receivers or making tackles, he intends to remain a part of the team.
"Maybe DBs can still come to my house and watch film," Foxworth said. "Maybe I can contribute in another way because if they win the Super Bowl, I want to wear the ring with pride and say I had something to do with it."