The bid will see Caesars pay 272p per share, stating that the William Hill board has indicated it would likely recommend the potential offer.
On Friday, William Hill confirmed that it had received separate proposals from both Apollo Management International and Caesars, with the operator clarifying that no offer had yet been made.
The operator also said that any offer is required to be made by 23 October, in accordance with UK takeover rules.
However, Caesars made clear that it would cut existing ties with William Hill if the operator chooses to accept any offer from Apollo, which includes a joint venture that sees Caesars currently own a 20% stake in William Hill’s US operations.
Caesars Entertainment CEO Tom Reeg said: "The opportunity to combine our land based-casinos, sports betting and online gaming in the US is a truly exciting prospect.
"William Hill's sports betting expertise will complement Caesars' current offering, enabling the combined group to better serve our customers in the fast growing US sports betting and online market."
Caesars said a combination would generate between $600m to $700m in net revenue in 2021. The proposed expansion follows Caesars' merger with Eldorado Resorts in July, which saw Eldorado acquire the operator for $17.3bn.
