ViacomCBS Inc. jumped as much as 5.8% on speculation that an activist investor will push for a shake-up at the company after the death of founder Sumner Redstone this week.

Credit Suisse Group AG, which in the past has made trades for investors who want to stay out of the spotlight, purchased 12.8 million ViacomCBS shares (VIAC) in the second quarter, noted Don Bilson at research and advisory firm Gordon Haskett.

That suggests an activist shareholder may be gathering a significant stake, looking to use the upheaval at ViacomCBS to press for a sale of the Paramount studio or perhaps the whole company, Bilson said in a report. Still, a seven-person trust led by Sumner’s daughter, Shari Redstone, has voting control over the company -- meaning any activist would need to win her over.

“There are limits to what an activist could do,” Bilson said. But the stock is low enough that an investor may see it as a good entry point, “especially if they believed that Redstone’s eventual passing would open up new opportunities,” he said.

In addition to the Paramount studio, the company’s holdings include the CBS broadcast network and cable channels such as MTV and Nickelodeon. ViacomCBS has been hurt by an advertising slump and cord cutting among cable customers, sending its shares down 36% this year through Thursday. Friday’s rebound sent the stock as high as $28.24 in New York.

But the company has already been making some changes. It has cut jobs as it integrates Viacom and CBS, two Redstone-controlled businesses that merged again in December after years of separation. It also plans to unload its Simon & Schuster publishing division and an office building in Manhattan.

And the media giant is looking to jump-start its streaming efforts by rebranding the CBS All Access platform. The new service could be called “Paramount+,” the Financial Times reported this week. ViacomCBS also mulled a sale of part of all of its Paramount studio lot in Los Angeles, with real estate firms or possibly Netflix Inc. seen as potential buyers, the newspaper reported.