Sierro was born in Sion, in the canton of Valais in the southwest of Switzerland. He is the son of former Valais State Councillor Serge Sierro.[3]
His father having played for Sierre and the Valais regional squad, and his grandfather amongst the founders of FC Crans-Montana, Sierro grew up in a footballing family.[3] Sierro joined the academy of FC Sion, in his hometown, in his youth.
Club career
Sierro began his senior career in the Swiss third division with the FC Sion B team during the 2013-2014 season. He made his debut with the FC Sion first team during the 2014-15 season. He scored his first goal on the 10 April 2016 against FC Thun.[4]
In January 2017, Sierro signed for SC Freiburg on a four-year contract. He did not find success at the club, and returned to Switzerland for the 2018–19 season, joining St. Gallen on loan.[5]
In June 2019, Sierro signed a four-year contract with Young Boys.[6]
In January 2023, Sierro signed for Ligue 1 club Toulouse.[7] Sierro was named club captain ahead of the 2023-24 season.[8]
Sierro was included in Switzerland's preliminary squad ahead of the UEFA Euro 2024 on 17 May.[12] He was named in the final 26-man squad on 7 June.[13] In said tournament on 15 June, Sierro appeared as an 86th-minute substitute for Remo Freuler in Switzerland's opening Group A fixture against Hungary.[14]
Career statistics
Club
As of match played 12 May 2024
Appearances and goals by club, season and competition