John Malone's Liberty Global is preparing to make a bid for Virgin Media, the UK cable operator with an enterprise value of more than $20 billion, in a deal that would mark the U.S. billionaire's biggest move yet into the UK and could set up a fresh clash with his former partner and rival Rupert Murdoch.

A bid could be announced in the coming days, according to several people familiar with the situation, and would come more than five years after Liberty Global first considered buying Virgin Media, in which Sir Richard Branson's Virgin Group still has a 3 percent stake.

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A successful bid for the UK's second-largest pay television operator would put Mr. Malone in direct competition with market leader BSkyB, which is controlled by Mr. Murdoch's News Corp. Virgin Media also offers telecoms services.

Mr. Malone and Mr. Murdoch have been both partners and competitors over the years. In the middle of the last decade, Mr Malone amassed an 18 percent holding in News Corp, the largest stake after Mr Murdoch, then swapped it for News Corp's interest in DirecTV, the U.S. satellite business.

Shares in Virgin Media, listed on the Nasdaq in New York, closed at $38.69 on Monday, giving the company a market capitalization of $10.4 billion. Its net debt was 5.7 billion at the end of the last quarter.

The deal has not been finalized and could still fall apart. Liberty Global and Virgin Media declined to comment.

(Read More: Strong Growth in Europe: CEO Liberty Global)

In November 2011, soon after the phone-hacking scandal forced News Corp to drop a bid for full control of BSkyB, Mr. Malone told the Financial Times that bankers had tried to "stir things up" but he would not bid against Mr. Murdoch for BSkyB.

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Liberty Global Set to Launch Bid for Virgin Media