Cotter is a product of Sion. In the 2018–19 season, Cotter scored 11 goals in 26 for the under-18s.[citation needed] Aged 17, Cotter played with the Sion U21 in the Swiss Promotion League.[2] In the beginning of December 2019, 17-year old Cotter began training with the first team.[2]
He made his official and professional debut on 8 December 2019, against Basel in the Swiss Super League; Cotter started on the bench, and replaced Seydou Doumbia in the 59th minute.[3] He also came on from the bench in the following league game against Neuchâtel Xamax.[citation needed]
Juventus
In the beginning of January 2020, Cotter was officially sold to Italian side Juventus.[4] Cotter reportedly signed a deal until June 2024, and was sold for a fee of around €4,9 million. He remained at Sion on loan for the rest of the season.[5] However, due to the suspension of football in Switzerland during the COVID-19 pandemic, he made no official appearances for the club in his loan spell.[citation needed]