(CNBC) - Shares of Whole Foods Market rocketed 28 percent on Friday after Amazon said it plans to acquire the grocery store chain for $42 a share, in a deal valued at $13.7 billion.

Amazon's offer represents a 27 percent premium to Whole Foods' closing price on Thursday. With Whole Foods shares trading around Amazon's offer price, investors appear to be speculating that another suitor could make a play for the grocery chain.

Among those who could potentially make a bid are Wal-Mart, who has been focusing its dealmaking on bulking up its digital business, and JAB Holdings, a private equity player that has been shifting its focus to restaurants and food and beverage businesses.