He was replaced by Chad Johnson 7:30 into the period.
Lehner was hunched over after he made a save against Senators forward Mark Stone and appeared to favor his left leg. Lehner skated off the ice but was helped to the bench by a trainer.
Lehner allowed a goal to Kyle Turris 30 seconds into the game; he finished with 11 saves on 12 shots.
Buffalo lost 3-1 at First Niagara Center.
Lehner was traded to Buffalo by Ottawa on June 26. He was playing his first game since sustaining a concussion on Feb. 16 in a game against the Carolina Hurricanes.
Stay Connected
NHL.TV™
NHL GameCenter LIVE™ is now NHL.TV™.
Watch out-of-market games and replays with an all new redesigned media player, mobile and connected device apps.
Introducing the new official NHL App, available for iPhone, iPad and Android smartphones and tablets. A host of new features and improved functionality are available across all platforms, including a redesigned league-wide scoreboard, expanded news coverage, searchable video highlights, individual team experiences* and more. The new NHL App on your tablet also introduces new offerings such as 60fps video, Multitasking** and Picture-in-Picture.
*Available only for smartphones
** Available only for suported iPads