'Time to say goodbye': Wall Street is giving up hope that another bidder will challenge Amazon for Whole Foods

Wall Street is giving up hope that another bidder will challenge Amazon's $13.7 billion deal to buy Whole Foods.

Gordon Haskett analyst Chuck Grom downgraded Whole Foods' stock to "neutral" from "buy" on Monday, saying a competitive bid is highly unlikely.

"It's been real, but time to say goodbye," Grom wrote in a research note. "We don't see another bid emerging."

Other investors appear to agree. Whole Foods' stock was trading around $42.62 - its lowest point since the acquisition was announced - on Monday morning.

The shift is a stark reversal from last week, when speculation soared that another challenger would step in and "do anything to either make this acquisition more costly for Amazon or prevent the asset from landing in Amazon's lap," as Barclays analyst Karen Short said at the time.

The fact that the stock is still trading above $42, which is what Whole Foods offered to pay per share for the company, shows that some hope remains for another bidder to emerge, however.

But that hope is waning after it was revealed Friday that Walmart, which has been frequently cited as a top contender to challenge Amazon for Whole Foods, isn't planning to offer a competing bid.

Grom says Kroger, another top contender, also appears to be an unlikely challenger following its announcement last week that its board had approved a $1 billion share repurchase program.

"The list of realistic buyers continues to shrink," Grom wrote.

Target and Food Lion owner Ahold Delhaize are among the only remaining potential bidders, and both seem unlikely, he said.

"Basing an investment decision solely on another bid ... seems irresponsible at this juncture," Grom wrote.