William Hill said “there can be no certainty” that any offer will be made.
According to UK takeover rules, Apollo and Caesars have until 23 October to make a firm offer.
Bloomberg was first to report that Apollo approached William Hill with a proposal. The written offer came on 27 August.
Apollo, a New York-based firm led by Leon Black, has made previous ventures into the gaming sector including a leveraged buyout with TPG of Harrah’s in the late 2000s.
William Hill is American sports betting partners with Caesars, a deal that dates back to the British bookmaker’s relationship with Eldorado Resorts.
In 2019 William Hill US agreed to serve as Eldorado’s sports betting operator for 25 years.
William Hill shares skyrocketed 43.2% in London Friday, setting a new intraday trading record. The company ended the day at £312.20 of $396.74.