SUNNYVALE — Activist investor Starboard Value has reinvigorated its noisy campaign urging Yahoo CEO Marissa Mayer to spin the company’s Asian assets back to shareholders, cut costs and merge with AOL.

The hedge fund’s manager, Jeff Smith, wrote a sharply worded letter Thursday to Mayer and Yahoo’s board of directors, expressing concerns about “rumors pervading the market” — many of them purely speculative — that the Sunnyvale Web company could use its huge stake in Chinese e-commerce giant Alibaba to buy a cable-TV network or pursue other costly acquisitions.

Smith warned of a “significant leadership change,” suggesting that he and other shareholders would push for Mayer’s ouster if she pursued what he called a “cash-rich split-off” allowing Yahoo to unload some its huge stakes in Yahoo Japan and Alibaba, which went public in September, in a way that allows Yahoo to make a big transaction without unlocking the full value of the assets.

Starboard’s stake in Yahoo is less than 1 percent, according to September public filings, but the New York firm has been a persistent and public critic of the company’s direction and sent a similar letter in September. It also made waves last year for orchestrating the overthrow of the board of Darden Restaurants, parent company of Olive Garden.

Smith said he met with Mayer on Oct. 27 and that she agreed with him that a cash-rich split-off was not the best idea.

Yahoo declined to comment on his letter Thursday. The company is likely to reveal more about the future of its Alibaba holdings later this month when it releases its quarterly earnings report.

In the meantime, Mayer has been moving ahead to revive and expand Yahoo’s core business. She plans to speak in San Francisco next month at the company’s first mobile developer conference, a chance to showcase its push into the mobile and video advertising market with recent acquisitions such as video advertising platform BrightRoll and mobile analytics and monetization firm Flurry.

But many analysts have been impatient with Yahoo’s series of acquisitions and hires, including of star TV news anchor Katie Couric a year ago, and do not believe the CEO has much longer to convince investors she is forging the right path ahead.

“Starboard’s view that Yahoo should not make any further expensive acquisitions is one I agree with,” said London-based analyst Cyrus Mewawalla of CM Research, which has advised selling Yahoo shares.

He said the company “has no clear direction and no clear vision on which space it wishes to occupy. It is a mishmash of Internet assets that do not appear to be paddling in the same direction. Its valuation is all about its stakes in Alibaba and Yahoo Japan rather than its core business, and nothing in the near term, in our view, is likely to change that.”

Contact Matt O’Brien at 408-920-5011. Follow him at Twitter.com/mattoyeah.