Billionaire activist investor Carl Icahn is building a stake in casino company Caesars Entertainment, sources familiar with the situation said.

The size of Icahn's stake is not immediately known.

Caesars shares jumped more than 5.5 percent on Friday. The shares dropped 46 percent last year.

Icahn did not immediately respond to a CNBC request for comment.

Last year, another billionaire proposed to make a deal for shares of the casino operator. Tilman Fertitta and advisors offered $13 a share in cash and stock, CNBC reported in October. Fertitta owns the Houston Rockets basketball team and the hospitality company Landry's, which includes Golden Nugget Casinos, Morton's steakhouses and the Rainforest Cafe.

Fertitta would have been chairman and CEO of the combined company, sources told CNBC at the time.

Casinos have become hot investment lately. The activist hedge fund Starboard Value has reportedly been building a modest stake in MGM Resorts International. MGM is on a cost-cutting initiative to boost profit by $300 million annually.

Last year, Icahn cashed out his stake in Tropicana Entertainment, selling it for $1.85 billion to Gaming and Leisure Properties and Eldorado Resorts. In 2017, he sold the shuttered Trump Taj Mahal casino in Atlantic City to Hard Rock International.