On Tuesday, Bull sold 121,615 shares at 105.88p each. The move comes just five days after investors cashed in their shares after Jefferies highlighted the challenges in the merger between Labrokes and rival Gala Coral.
Jefferies suggested Coral is "not a perfect fit" to help Ladbrokes grow its struggling online sports business, which sent shares down 1.89p to 104.71p last Thursday. Ladbrokes and Coral are looking to create the UK's biggest bookmaker.
However, Jefferies analyst Ian Rennardson believes the two companies will have to sell about 600 of their 4000 betting shops to appease the competition watchdog.