Early years A
forward, Forss began his career in his native Finland with spells at FC Ruskon Pallo,
TuWe and the FDS-Suomi football school. At age 13, he moved to England to join the
academy at
Premier League club
West Bromwich Albion and progressed to sign a two-year scholarship deal in 2015. He was called into the U21 squad for two
EFL Trophy matches in the first half of the
2016–17 season and made one appearance, Forss was released when his scholarship ended in May 2017.
Brentford 2017–2019 On 22 June 2017, Forss joined the
B team at
Championship club
Brentford on a two-year contract. He finished the 2017–18 season as the B team's top scorer with 21 goals and won both of the team's Player of the Year awards. Forss was promoted into the first team squad for the
2018–19 season and despite missing five months of the campaign with a back injury, he was a regular inclusion in matchday squads when fit and finished the season with 9 appearances and two goals. He scored seven goals in his first seven appearances for the club and scored the first senior
hat-trick of his career in a 4–1 victory over
Southend United on 12 October. Four further goals in December 2019 saw him nominated for the
League One Player of the Month award. By the time his spell was ended early by a season-ending torn hamstring on 14 January 2020, he had scored 11 goals in 19 appearances. Forss' performances during the season were recognised with the AFC Wimbledon Young Player of the Year award.
2020–21 season Following surgery on his torn hamstring, Forss returned fit for the
2020–21 season and the departures of
Ollie Watkins and
Saïd Benrahma elevated him to second-choice behind new signing
Ivan Toney. For two-thirds of the season he served predominantly as a substitute, Off the back of a spell of seven goals in 13 appearances, In April 2021, a change in formation allowed Forss to break into the starting lineup, His first appearance as part of the new formation saw him score his first goal for over five months, in a 5–0 win over
Preston North End. Forss scored the 81st-minute goal which secured a 3–2
aggregate victory and sent the Bees to a second consecutive playoff
Final. Forss' 2020–21 season ended with 50 appearances, 10 goals and promotion to the Premier League after a 2–0 victory over
Swansea City in the playoff Final. Forss'
2021–22 EFL Cup performances were later recognised with a place in the Team of the Tournament and his five goals scored in the tournament tied him with
Eddie Nketiah as top-scorer. By the final day of the winter
transfer window, Forss had scored six goals in 12 appearances, but with no goals in seven Premier League appearances. He scored 19 goals in 74 appearances during four seasons as a first team player with the club. reported to be £3 million. He scored his first goal for the club on his second appearance, in a 3–2 defeat to Queens Park Rangers on 6 August 2022. Forss ended a three-month goal drought. he scored five goals in 9 appearances. Forss had scored 10 goals in 42 appearances. Forss made 23 appearances and scored seven goals during the
2023–24 season, which kept him out for the opening seven weeks of
2024–25. He made four substitute appearances before suffering a setback, which caused him to miss six weeks. He scored five goals in 25 appearances, ==International career==