Assan had his highlight while playing with FC Zürich in the 2021–22 Swiss Super League where he helped the team win the title by scoring 20 goals and ending the season as 2nd best top-scorer of the league that season,[4] and in third place as best assistant.[5] This made him one of best players of the Swiss League and called the attention of many clubs worldwide to sign him.
On 16 June 2022, Ceesay agreed to join newly promoted Serie A club Lecce on a two-year contract, with the option of a third, from 1 July when his contract with FC Zürich would expire.[6][7] On 14 August 2022, Ceesay scored on his league debut as Lecce was condemned to a 1-2 defeat against Inter Milan at Stadio Via del mare.[8]