Schüller began his career at FC Kasiysi, a club based in his hometown Espoo. Later he moved on to rivals HooGee.
FC Honka
Schüller made his debut in an FC Honka jersey during the 2008 Finnish League Cup. He played in his first Premier Division match in August 2008 against RoPS.[2] In December 2008, Schüller signed a contract with Honka that would have kept him in Espoo until the end of the 2011 season.[3]
Schüller scored his first league goal for FC Honka in June 2009, less than a week after his 18th birthday, when his team came out victorious from a match against Kuopion Palloseura.[4] Schüller scored on his debut in European club competitions, netting his team's second goal of the game when FC Honka beat Welsh side Bangor City FC in the Europa League on 16 July 2009.[5] In August 2009, Schüller scored his second league goal for FC Honka and was named man of the match when he helped his team to a 3–1 victory over Tampere United.[6]
On 22 September 2009, it was announced that Schüller had put pen to paper for a new deal until the end of the 2012 season.[7]
HJK
In February 2012, HJK announced the signing of Schüller from FC Honka, along with teammate Demba Savage, for a fee of €200.000.[8] Qualified for the Europa League group stages 2014 with HJK with a 5-4 aggregate victory over SK Rapid Wien.
BK Häcken
On 7 October 2015, Schüller agreed to transfer to Swedish Allsvenskan side BK Häcken for the 2016 season.[9] Schüller was then joined at BK Häcken by HJK teammate Demba Savage on 28 October 2015.[10]
Minnesota United
On 24 January 2017, Schüller signed with Minnesota United,[11] for a reported fee of $750,000.[12]
Schüller was released by Minnesota at the end of their 2019 season.[13]
Return to HJK
On 9 August 2017, Schüller rejoined HJK on a loan deal until the end of the season.[14]
After his contract expired with Minnesota in the end of 2019, he signed a permanent deal with HJK.
Djurgården
In the end of 2020, Schüller returned to Allsvenskan and joined Djurgården.[15] The transfer fee was not disclosed, but it was accordingly to the clause in his contract with HJK, concerning any transfer abroad.[16]
On 8 January 2022, Schüller extended his contract with the club on a new deal until the end of 2025.[17] On 1 April 2024, in the opening game of the 2024 season, Schüller suffered a surgery-requiring foot injury by a tackle by Kolbeinn Þórðarson, and was estimated to be sidelined for months.[18] On 25 July, he made his first appearance after recovering from the injury, in a 3–0 UEFA Conference League qualifying win against Progrès Niederkorn.