The $10 billion battle for control of UK supermarket chain Morrisons is coming to a head.

And it looks set to be decided with a rarely used auction process.

It will be a contest between two U.S. private equity outfits: Fortress Investment Group versus Clayton, Dubilier & Rice.

Last month Morrisons accepted a $9.6 billion bid from CD&R.

But Fortress could still trump that offer.

Now Morrisons says it's in talks with regulators over an auction.

It says that would take place on a date set by the official Takeover Panel, which governs mergers and acquisitions in the UK.

After the auction, Morrisons shareholders would vote on whether to accept the winning bid.

CD&R's latest offer is a 60% premium to Morrisons' share price before takeover interest emerged in June.

Fortress says it's still weighing up its options.

On Wednesday (September 8) afternoon Morrisons shares were trading above the level of the CD&R bid, indicating that investors expect a higher offer.