*Club domestic league appearances and goals, correct as of 17:26, 10 November 2024 (UTC) ‡ National team caps and goals, correct as of 23:14, 17 November 2024 (UTC)
Grillitsch joined Werder Bremen on 1 July 2013. He split the 2013–14 season between the Werder Bremen U19's youth team and Werder Bremen II.[1] He made 15 appearances in the A-Junioren-Bundesliga Nord/Nordost scoring 11 goals[2] and made five appearances in the Regionalliga Nord for Werder Bremen II.[2] In the 2014–15 season, Grillitsch made 26 appearances scoring nine goals for Werder's reserve team.[3]
2015–16 season
Grillitsch made his first team debut during the 2015–16 season.[4] He played the full 120 minutes including extra-time in the 2–0 win against Würzburger Kickers in the first round of the DFB-Pokal on 8 August 2015, notably assisting Anthony Ujah for 1–0.[5] His first Bundesliga match was a 3–0 loss to Schalke 04 on matchday one on 15 August 2015. He replaced the veteran Clemens Fritz after 70 minutes at 2–0.[6] He also played for Werder Bremen II during the 2015–16 season.[4] Grillitsch achieved his first assist in the Bundesliga as Werder beat Mainz 3–1 on 24 October 2015 setting up Fin Bartels for the third goal. He played the full 90 minutes.[7] Four days later, Grillitsch prominently featured in Werder's 1–0 second-round DFB-Pokal victory over 1. FC Köln, providing a major goal-scoring chance for Ujah, playing multiple through-balls and almost scoring.[8][9][10] Afterwards, he was voted "Man of the match" by the club's fans.[11]
2016–17 season
On 18 March 2017, Grillitsch scored his second goal of the 2016–17 season in a 3–0 win against Leipzig, a match that saw all three of Werder Bremen's Austrian players score in the club's highest win of the season.[12][13]
He made his debut for the club in the league match against Bayer 04 Leverkusen (1–1 draw) on August 26, 2017. Grillitsch scored his first goal for 1899 Hoffenheim on November 2 that year in the UEFA Europa League against Istanbul Başakşehir. However, Hoffenheim finished last in the group behind Istanbul Başakşehir, SC Braga and PFK Ludogorets.
Things went better in the Bundesliga, with a fourth-place finish in 2017-18, and a group stage spot in the UEFA Champions League. The following seasons, Grillitsch finished eighth, seventh, eleventh and eighth again with Hoffenheim, in his five seasons at the club, where he clocked up 151 appearances with eight goals and eleven assists.
Grillitsch was a starter in the vast majority of those matches. But in the summer of 2022, Grillitsch let his contract expire with the club.
Ajax and Hoffenheim again
After moving to then Dutch champions AFC Ajax in the summer of 2022, returned to Hoffenheim after a year when the Amsterdam giants suffered a poor season with a third-place finish.