CME Group, the world’s largest futures exchange, has suffered the departure of a senior sales executive at its Chicago clearing house, at a crucial juncture in the battle for buyside business between global clearers.

Tina Lemieux, a managing director in CME's Chicago office who oversaw hedge fund and retail sales at CME Clearing, is understood to have left her role this month, according to people familiar with the matter. No direct replacement is understood to have been named yet. A CME spokesman declined to comment. Lemieux could not be reached for comment.