Amazon's rivals 'will do anything' to make the company pay more for Whole Foods

Amazon may have to put up a fight for Whole Foods.

Speculation on Wall Street is growing that another bidder could counter Amazon's offer of $13.7 billion, or $42 a share, for the natural and organic grocery chain.

"Many will do anything to either make this acquisition more costly for Amazon, or prevent the asset from landing in Amazon's lap," Barclays analyst Karen Short wrote in a research note.

Whole Foods' shares closed at $43.22 a share on Monday, about 3% over Amazon's offer price, indicating that investors are rallying around the theory that another bidder is getting ready to pounce. The company's stock was trading around $42.95 on Tuesday morning.

Short identified Walmart, Kroger, and Target as potential bidders and raised her stock price target more than 14% over Amazon's bid to $48 - though she said the company could be sold for as much as $57 a share.

"In theory, all retailers that sell food and compete with Amazon because we think most have too much to lose not to bid," she wrote.

Oppenheimer analyst Rupesh Parikh seems to agree. He raised his price target for Whole Foods to $45.

"Another bid cannot be ruled out even from a defensive measure to protect against the Amazon threat," he wrote in a research note.

Whole Foods would owe Amazon a $400 million break-up fee if it breaks the deal for a competing bid.

But a strategic retail bidder, such as Walmart, could achieve up to $600 million in potential cost savings that could make the Whole Foods deal more profitable than it would be to Amazon, according to Short.