CMA has launched its first investigations under new consumer powers, examining how major ticketing, driving school, gym and homeware brands present fees and time-limited offers online.
The facilities are in the states of Wisconsin, Maryland and Florida.
Talks remain at an early stage and no final valuation or deal size has been set.
Melissa Stone has been appointed as his interim replacement.
The family sold 64 million shares for R1.6bn ($93.06m).
Campbell spent a decade at adidas, including serving as its North America president.
