LeClair is scheduled to undergo tests on Friday, but Flyers Coach Ken Hitchcock confirmed Thursday that LeClair will miss "significant time."
The injury occurred when LeClair was checked by defenseman Marc Bergevin and fell into the boards in the Penguins' zone with just over six minutes remaining in the first period.
"We just have to hope there is no ligament damage," Hitchcock said. "If there is ligament damage, then we have some things to worry about. We just have to pray that we can avoid surgery."
With just 16 goals in their last 11 contests, the Flyers will be hard-pressed to replace LeClair's team-leading 11 tallies. Jeremy Roenick had a goal and an assist Wednesday to raise his total to 18 points, one more than LeClair.
The 33-year-old LeClair has 352 career goals, including 303 in 560 games with the Flyers.