Genk Early years Sierra, with a Spanish grandfather and an Italian grandmother on his father's side, was born in
Hasselt, Belgium, and spent his early years in
Zonhoven. He started playing football at local club Melosport Zonhoven and later moved to
Sporting Hasselt, following in the footsteps of his older brother. Sierra continued his development through Genk's youth teams and signed his first professional contract in August 2017, at the age of sixteen. In the 2019–20 season, he played with Genk's youth team in the
UEFA Youth League.
First team During the
2019–20 season's winter break, first-team coach
Hannes Wolf selected Sierra for winter training camp in
Benidorm. Sierra's exceptional performance during this period earned him a permanent place in the first team, and his contract was extended until 2023. He was assigned jersey number 16. On 13 February 2020, he appeared on the bench for the first time in the away match against
Antwerp. Sierra made his official debut for the first team on 14 September 2020, during the league match against
Beerschot, replacing
Eboue Kouassi in the 81st minute as Genk were defeated 5–2. Following the death of former Genk player
Anele Ngcongca in November 2020, Genk decided to change Sierra's jersey number to 19, as they opted not to assign the number 16 to any other player out of respect for Ngcongca. Sierra made only one senior appearance for Genk, before leaving the club in January 2021. He made his debut for the club on 4 April 2021, replacing
Orestis Kiomourtzoglou in the 65th minute of a 3–0 loss to
PSV. Sierra faced challenges in meeting expectations during his time at Heracles. Over one and a half seasons in the
Eredivisie, he earned five starts and came on as a substitute in 16 matches. Following the club's relegation in 2022, he made 17 brief substitute appearances in the
Eerste Divisie. Despite an ongoing contract, he was told to find a new club.
VVV-Venlo On 25 July 2023, Sierra signed a two-year contract with
VVV-Venlo in
Eerste Divisie, with an option for an additional season. He made his debut for the club on the first matchday of the
season, starting and playing 65 minute of a 3–1
Limburg derby loss to
MVV. On 15 December, he scored his first competitive goal for VVV in a 2–1 league loss against
TOP Oss. He remained with the club through the
2024–25 season. Upon the expiry of his contract, VVV-Venlo opted not to renew, and Sierra left the club as a free agent.
Sporting Hasselt In January 2026, after six months as a free agent, Sierra returned to his hometown and youth club
Sporting Hasselt competing in
Belgian Division 1. ==International career==