KITZBUEHEL, Austria (AP) — Tommy Haas hinted at cutting short his farewell season and retiring immediately after losing to fellow German player Jan-Lennard Struff 6-3, 7-6 (4) in the opening round of the Generali Open on Tuesday.

"It's a terrible feeling. It could well be that this was my last match," said the 39-year-old Haas, who was once ranked No. 2. "I am not playing anymore what I am capable of. And that is disappointing. It's my job to go out there and win matches."

Ranked 248th, Haas entered the final clay-court event of the year on a wild card. He is 6-14 this year, having lost all six matches since upsetting Roger Federer in Stuttgart in June.

Struff joined fellow German Philipp Kohlschreiber in the second round. The 2015 champion beat Facundo Bagnis of Argentina 7-5, 3-6, 6-3, three days after pulling out of his semifinal in Hamburg with a thigh injury.

Kohlschreiber next plays seventh-seeded Jiri Vesely, who defeated Yannick Hanfmann of Germany 6-4, 6-4.

Also, Colombian qualifier Santiago Giraldo upset two-time former champion Robin Haase of the Netherlands 7-6 (6), 4-6, 6-4; and Horacio Zeballos of Argentina saved four match points in the second set before beating Rogerio Dutra Silva of Brazil 2-6, 7-6 (11), 7-6 (4).

Gerald Melzer of Austria, a semifinalist last year, and Renzo Olivo of Argentina also advanced to the second round.