Tight end was among the Nittany Lions' deepest positions just last month. But Brent Wilkerson suffered a serious back injury, and Lehman and Carter players suffered injuries Saturday against Syracuse.
O'Brien said he wasn't certain if Carter could play Saturday versus Eastern Michigan. If he can't, that means redshirt freshman Jesse James would be the top option, with true freshman Adam Breneman as the No. 2. The only other tight end listed on the roster is true freshman walk-on Tom Pancoast.
"Certainly, any time you have a player of the caliber as Matt Lehman go down, it's not a good thing," O'Brien said. "It definitely falls into the category of 'next man up.' "
O'Brien didn't disclose the exact injuries of Lehman or Carter. But with Lehman, he referred back to Michael Mauti's knee injury. O'Brien believed Lehman still had a future in football. Carter also remained on the sideline Saturday with his arm wrapped up.
As a result of those injuries, O'Brien said he might utilize another position a bit more -- such as fullback Pat Zerbe or another wideout -- to make up for the loss.
"You have to have a contigency plan," O'Brien added.
Lehman was fourth on the team in receiving last season with 24 catches for 296 yards and three touchdowns. He had two catches for 17 yards against Syracuse.