The 39-year-old reacted slowly to the first of Bilal El Khannouss’ brace and failed in his attempt to push away a low strike from Jamie Leweling.
The Danish goalkeeper has faced scrutiny over his displays since returning from a shoulder injury last season, as well as after scoring an own goal in Celtic’s Scottish Cup final loss to Aberdeen.
Benjamin Nygren had momentarily drawn Celtic level in the first half, but the Bundesliga outfit proved convincing victors in the first leg of the knockout round play-offs, with Tiago Tomas compounding a disappointing evening for Celtic with a stoppage-time finish.
Celtic overcame Stuttgart en route to the 2003 UEFA Cup final under current manager Martin O’Neill, but the 73-year-old’s attention is now likely to turn to domestic matters, even with next week’s return leg in Germany looming.
That fixture marks the beginning of a demanding stretch of four away matches in 10 days, during which Celtic will make two visits to Ibrox either side of a journey to Aberdeen.
