Urban, the team's fourth-round pick out of Virginia, went down after a block by offensive tackle Jah Reid in a drill less than an hour into practice. He couldn't put any weight on his right leg and needed a trainer under each arm to get off the field.
An MRI is scheduled for Urban on Wednesday night.
"We'll just hope and pray for the best on that one," coach John Harbaugh said.
This is the first significant injury of Ravens camp (unless cornerback Lardarius Webb's back issue becomes more severe) but it's not the first injury of the year for Urban. He was limited for the early offseason workouts after undergoing ankle surgery in February.
But Harbaugh hasn't completely ruled out Urban for the season.
"I'm still hopeful that he'll be back, but we'll have to see," Harbaugh said.
The sixth practice of training camp featured a play that nearly cost the Ravens two rookies on the defensive line. On the same drill where Urban was injured, defensive tackle Timmy Jernigan had to leave the field as well.
Jernigan, a second-round pick from Florida State, appeared to hurt his back. He went inside the team facility without any assistance from trainers.
"Timmy looks fine," Harbaugh said.
Defensive line is one of the positions where the Ravens can absorb a hit to their depth. Outside of the starters (Canty, Haloti Ngata and Brandon Williams), the Ravens have intriguing backups in Jernigan, Lewis-Moore and DeAngelo Tyson.
While the Ravens were expecting a huge impact from Urban, a major injury could curtail his development. Urban likely would have a shot at starting next season.
He is the perfect fit for a 3-4 defensive end, which is also referred to as "five technique." At 6-foot-7, 298 pounds, he has nearly the same build as Canty (6-7, 317) but has more upside.
“Brent has made steady progress since the first day he walked in here,” defensive line coach Clarnece Brooks said. “We liked him when we drafted him and after he was here for a couple days we knew exactly what we liked about him. He’s a great kid, works hard.”