The Lions lost tight end Brandon Pettigrew, the No. 20 overall pick in the draft, to a left knee injury on their first series.
"That's something that'll need some serious looking at," Schwartz said.
Pettigrew's knee buckled on a noncontact play, as he was maneuvering to make a block.
Asked if initial tests had shown a torn ligament, Schwartz said: "I don't want to read too much into it."