Without revealing the nature of the injury, coach Dan Bylsma said the initial prognosis is that the injury is not a short-term one.
Lehner was untouched when he went down in his crease. Though he left the ice favoring his left leg, he was spotted wearing a protective boot on his right ankle.
Lehner allowed one goal on 12 shots and was replaced by Chad Johnson, who gave up a goal on nine shots.
Buffalo gave up a first-round draft pick to acquire Lehner in a trade with Ottawa in June. He was playing his first game since suffering a season-ending concussion in a 6-3 loss to Carolina on Feb. 16.
Information from The Associated Press was used in this report.