Amid deafening criticism by sports writers and on talk radio, a worried Mr. Rodriguez called Mr. Buffett, say people familiar with the matter. The two had become friends a few years ago, after the slugger flew to Omaha to meet with the investing guru and rabid baseball fan. After that, the two met socially several more times, say the people familiar with the matter. Signifying their mutual admiration, an autographed Rodriguez jersey hangs at Berkshire Hathaway's Omaha headquarters.

Mr. Buffett's advice was simple, says a person familiar with the matter: approach the Yankees solo, without Mr. Boras. "A-Rod really loves being a Yankee," says Mr. Buffett. He declined to comment on the substance of any conversation with Mr. Rodriguez, saying he doesn't discuss private talks.