Williams filed suit in Manhattan Supreme Court saying John and Vicki Andrinopoulos signed a contract July 21 to purchase his penthouse, the New York Post said.
The contract called for a $282,500 down payment and additional down payments of $20,000 a month until mid-October, when the purchase was to be closed, the lawsuit says.
Williams charges the couple refused to set a closing date in October, then defaulted on their next $20,000 payment.
Williams is seeking to keep the $342,500 being held in escrow by his lawyer and also wants the couple to pay his legal bills, the Post said.
None of the parties involved in the suit would comment, the Post said.