He played as a left-back and was engaged in a sequence in which the opposing goalkeeper parried his shot, resulting in Germán Cano's rebound goal.

[3] In his eighth appearance for Fluminense, Alexsander scored his first professional goal in a 7–0 victory over Volta Redonda on March 8, during the tenth round of the 2023 Campeonato Carioca.

Nearing the conclusion of his recuperation, he sustained another injury on June 13, damaging his right thigh, delaying his return to the field by three months.

[14][15] He was part of the squad that won the Copa Libertadores for Fluminense, the club's first-ever title in the competition, defeating Boca Juniors 2–1 at the Maracanã.

[18] In April 2024, Fluminense banned Alexsander, along with teammates John Kennedy, Arthur, and Kauã Elias, for disciplinary difficulties.