Yahoo, facing billionaire investor Carl Icahn’s attempt at a corporate coup, reportedly is racing to complete an advertising deal with Google that could short-circuit efforts to force a union with Microsoft.

The New York Post, citing two unnamed sources, said Yahoo could announce a deal next week on an “open platform” through which Google, Microsoft, AOL and others could bid for the right to serve ads linked to keyword searches.

An open system could help such a deal pass regulatory muster even though Google, which dominates search-engine advertising, would be expected to win the lion’s share of bids for advertising on Yahoo’s sites.

In April, Google also overtook Yahoo in U.S. traffic for the first time, according to comScore. Google sites had 141.1 million unique visitors to secure the No. 1 ranking, while Yahoo’s 140.6 million put it at No. 2, followed by Microsoft’s 121.2 million.

In an open letter, Mr. Bostock said that Mr. Icahn’s plan to run a 10-member slate in opposition to Yahoo’s incumbent board of directors reflects “a significant misunderstanding” of the Microsoft offer.

“Conversely, we do not believe it is in the best interests of Yahoo! stockholders to allow you and your hand-picked nominees to take control of Yahoo! for the express purpose of trying to force a sale of Yahoo! to a formerly interested buyer who has publicly stated that they have moved on,” he said.

Yahoo’s board, comprised of nine independent directors and Mr. Yang, has met more than 20 times since Microsoft’s initial $31 per share offer on January 31, he said. Eventually, negotiations stalled when the sides could not bridge the gap between Microsoft’s revised $33 per share offer and Yahoo’s asking price of $37 per share. On May 4, Microsoft CEO Steve Ballmer said he was withdrawing the $33 per share offer.

In a separate letter, Mr. Yang exhorted Yahoo employees to disregard the uncertainty caused by high-level maneuvering. Analysts have speculated that uncertainty could prompt some employees to jump ship.

In mid-morning trading, shares of Yahoo shed $.22, or .8 percent, to $27.53, while Micosoft fell $.31, or 1 percent, to $30.14.

Mr. Icahn, who often takes stakes in troubled companies like Motorola and Time Warner and then agitates for change, on Thursday unveiled 10 candidates to dislodge Yahoo’s incumbents. Included on the slate are Mr. Icahn, Mark Cuban, the owner of the Dallas Mavericks, and Adam Dell, of Impact Venture Partners.