Tommy Haas has hinted he could call time on his career early following a disappointing straight-sets defeat to Jan-Lennard Struff at the Generali Open.

Haas, 39, is due to retire at the end of the ATP season but, after his 6-3 7-6 (7-4) defeat on Tuesday, he suggested he may quit now due to what he perceived as a performance well below his best.

"It's a terrible feeling, it could well be that this was my last match," he told a media conference.

"I am not playing anywhere near what I am capable of and that's disappointing.

"It's my job to go out there and win matches."

Despite his obvious disappointment, Haas was far from outclassed by the sixth seed and had multiple opportunities to break Struff in the opening set.

He was unable to make them count, though, and his first-round exit was confirmed after a tie-break that Struff controlled.

Haas was not the only one licking his wounds as two-time champion Robin Haase was also an early casualty, the Dutchman losing 7-6 (8-6) 4-6 6-4 to Santiago Giraldo.

There were fewer problems for Jiri Vesely, who beat Yannick Hanfmann 6-4 6-4, while Horacio Zeballos - the eighth seed - came from a set down and saved four match points on his way to victory over Rogerio Dutra Silva.

Philipp Kohlschreiber - another former champion - defeated Facundo Bagnis 7-5 3-6 6-3 despite recent injury concerns, and there were also wins for Renzo Olivo and Gerald Melzer on Tuesday.