Hazard is expected to follow in the footsteps of his more celebrated elder brother Eden by joining the Blues this summer and his Ligue 1 employers appear to have accepted the move is inevitable.
Sibierski told his club's official website: "It should be official tomorrow. (When I arrived) there was no intention of letting him go and I met him very quickly after my arrival to show my confidence in him."
He added: "He still had one year left and it was proposed he extended it but he told me eye to eye that did not interest him and he wanted to leave Lens.
"I realised 48 hours later why, when I learned Chelsea wanted him. I understand."
Lens coach Jean-Luis Garcia also accepted there was no chance of keeping Hazard.
He added: "He is a boy of 19, his elder brother signs for Chelsea and he is urged to do so by the same club, who won the Champions League.
"Congratulations to Thorgan. Unfortunately we cannot go against such an opportunity. Good luck to him."