In December, Disney struck a $52.4 billion, all-stock deal to buy much of 21st Century Fox’s assets. Now, Comcast plans to announce its own offer for 21st Century Fox’s assets as early as Wednesday, according to two people familiar with the matter who spoke on condition of anonymity to discuss company business. Shares of 21st Century Fox jumped more than 7 percentage points in early trading Wednesday. Comcast’s stock price fell about 3 percent, while Disney gained about 1 percent.

The contest will pit Brian L. Roberts, the chief executive of Comcast, against Disney’s Robert A. Iger in what could be a fierce bidding war for a significant chunk of Rupert Murdoch’s media empire.

[Read about the AT&T-Time Warner ruling here.]

Comcast, which already owns NBCUniversal, has put together a bid of slightly more than $60 billion in cash and contractual assurances that Fox would be paid what is known as a reverse breakup fee — perhaps as much as $2.5 billion — in the event a transaction is blocked by the government, the people said. But any regulatory concerns may be allayed by the straightforward approval of the AT&T-Time Warner deal. Judge Richard J. Leon of the United States District Court in Washington said the agreement could go through without either company divesting any assets.

It is hard to overstate how closely Comcast was monitoring the situation. Executives at NBCUniversal had dispatched people to wait in the courtroom to hear the verdict. Mr. Roberts waited at his executive offices at Comcast’s headquarters in Philadelphia, tuned to CNBC and keeping an eye on Twitter. According to a person familiar with the matter, Comcast’s board met Tuesday evening to discuss its revamped bid for Fox, which rebuffed an overture last year.

[The AT&T-Time Warner case showed the need to reboot antitrust law, our columnist writes.]

In November, Mr. Roberts traveled to Mr. Murdoch’s estate in the Bel-Air neighborhood of Los Angeles, according to two people familiar with the meeting who spoke on condition of anonymity because it has not been made public. There, over glasses of wine produced from vineyards on the estate, Mr. Roberts broached the possibility of Mr. Murdoch making a deal with Comcast. Mr. Murdoch explained that talks with Disney had already begun, but that the companies were still $4 billion apart on price.