Natural and organic food retailer Whole Foods Market Inc. on Friday extended its tender offer for Wild Oats Markets Inc. for a fourth time as it waits for a hearing that will decide if it can go ahead with the deal.

The offer to acquire all of Wild Oats' outstanding shares for $18.50 each, or about $565 million, will now expire on August 10, instead of July 20 as previously announced.

The largest U.S. organic grocer said in February that it planned to buy Wild Oats to better compete with larger traditional grocers, which are increasingly encroaching into its organic and prepared foods niches.

But the U.S. Federal Trade Commission filed a suit to block the deal on concerns it would eliminate competition in many local markets around the United States. It sought a temporary restraining order and preliminary injunction.

A hearing in U.S. District Court for the District of Columbia on the injunction is scheduled to conclude on August 1.

Whole Foods said that as of Thursday, 17,049,990 Wild Oats shares, or 57 percent of those outstanding as of April 27, had been tendered and not withdrawn.