Gattermayer began his youth career with
Austria Wien before joining
Floridsdorfer AC in March 2014. Ahead of the 2016–17 season, he moved to the academy of
Admira Wacker. He made his debut for Admira's
reserve team in the
Regionalliga in October 2020 against
FC Mauerwerk, making two appearances before the season was cancelled due to the
COVID-19 pandemic. In May 2021, he made his professional first-team debut in the
Austrian Bundesliga, coming on as a substitute for
Josef Ganda in the 81st minute against
Rheindorf Altach on matchday 32 of the
2020–21 season. He made 14 top-flight appearances before Admira's relegation to the
2. Liga in 2022. In the
2022–23 season, he made 25 appearances and scored six goals. He made his debut on the opening matchday in a 2–0 defeat to
1860 Munich but did not feature again. In February 2024, he returned to Austria on loan to 2. Liga side
SKU Amstetten, where he made 14 league appearances and scored three goals. He cited manager
Dietmar Kühbauer's belief in him as a key factor in his decision, stating that he was determined to prove himself again at the top level. In March 2025, Gattermayer scored the deciding goal in the final of the
2024–25 Austrian Cup, helping Wolfsberger AC to their first ever cup title. ==Personal life==