Daniel Altmaier was eliminated in the first round of the lawn tournament in Halle, Westphalia.
The 23-year-old tennis pro from Kempen lost against the Australian Nick Kyrgios 3: 6, 5: 7 and was largely without a chance.
Kyrgios, who caused a scandal in the semifinals against Brit Andy Murray last week at the tournament in Stuttgart and then complained of racist insults against himself, converted his second match point after 67 minutes.
So far, no German has made it into the round of 16 at the event, which is endowed with 2.275 million euros. On Monday, local hero Jan-Lennard Struff and German champion Henri Squire were eliminated in the first round.
Olympic champion Alexander Zverev had to cancel his participation because of the serious foot injury he suffered at the French Open.
Oscar Otte from Cologne still has a chance of progressing on Tuesday evening. The German number two meets the Serbian Miomir Kecmanovic in his opening match.