In the summer of 2018, he moved to Basel's youth department and in 2022 he advanced to their U-21 team, but remained part of the U-18 team that celebrated winning the Swiss championship at the end of June 2023.
In July 2023 he signed a professional contract and advanced to their first team for their 2023–24 season.
[1] After playing in three test games Avdullahu played his domestic league debut for the club in the home game in the St. Jakob-Park on 13 August 2023 as Basel were defeated 2–1 by Lausanne-Sport.
[2] In the 2023–24 Swiss Cup second round match, on 16 September, Avdullahu scored his first goal for the team as Basel went on to win 8–0 against amateur club FC Bosporus in Bern.
On 15 November 2023 he was called up into the Switzerland U-21 squad, however, remained both matches on the bench as unused substitute.