A massive renovation plan announced for the U.S. Open site will not include a roof over center court and instead focus on new courts and increased seating, the U.S. Tennis Association (USTA) said on Thursday.

The last four U.S. Open championships finished on a Monday instead of Sunday because of rain delays, raising a clamor for a covered center court to help keep the schedule on track but the improvement plan does not address that issue.

The project, expected to cost hundreds of millions of dollars, will be undertaken by the USTA, which said logistical issues stood in the way of putting a roof over Arthur Ashe Stadium, the world's largest tennis stadium.

The decision means the U.S. Open will soon be the only grand slam event without rain protection. Center courts at Wimbledon and the Australian Open have retractable roofs, while the French Open has announced plans to cover its main court.

The new plans call for replacing Louis Armstrong Stadium with a venue that would expand seating 50 percent to 15,000.

The grandstand court would be torn down and moved to another area at the National Tennis Center with a capacity of 8,000, up 33 percent from the current setup.

Other improvements include a viewing deck that would allow spectators to watch players practice in one direction and view tournament matches on courts facing the other way.

(Reporting By Larry Fine in New York; Editing by Frank Pingue)