Bats Global Markets has quietly begun searching for a new president just over a month after it forced William O'Brien out of the position, according to people familiar with the matter.

After O'Brien abruptly departed Bats in July, Bats chief executive Joe Ratterman assumed the title of president "effective immediately," according to a statement at the time. Ratterman is based in Lenexa, Kansas, while O'Brien worked out of the firm's Jersey City, N.J. office.