Tight end Dennis Pitta appears to have a broken hand and could miss the entire preseason.
The injury occurred during Monday's padded practice.
"It looks like he broke his hand," Head Coach John Harbaugh said. "It looks like he'll have to get it repaired in some form or fashion and he should be back for the first regular-season game. That's very tentative, I'm very ahead of myself."
Pitta will have an MRI on Tuesday to further assess the damage, and the Ravens will be able to tell more accurately at that point how much time he will miss.
If he ends up missing significant time, it would be a significant blow to the offense. Last season he was the team's top tight end down the stretch and caught four touchdown passes in the final eight games.
Pitta became one of quarterback Joe Flacco's most consistent targets and finished the regular season with 40 catches for 405 yards and three touchdowns. He added seven more grabs for 70 yards and a touchdown in the two playoff games.
"He's definitely an important part of our offense," veteran receiver Anquan Boldin said. "I think you saw last year him play a big role, especially when it came down the stretch. Dennis is a guy that can play inside, a guy that we can line up outside, get different mismatches. He's a nightmare for defenses."
In Pitta's absence, Davon Drew took most of his reps. Drew has spent the last two seasons on the Ravens practice squad.
The Ravens also still have third-year tight end Ed Dickson, who had 54 catches for 528 yards and five touchdowns last season.
"We've got to step it up," Dickson said. "It's just like when Todd Heap went out. We didn't know who was going to be the starter.
"Losing that competition out there, the young guys are going to have to step up. I'm going to have to motivate myself. I'm always working hard, but it was easy having that guy putting pressure on me."