England Rugby 2015 had expected to agree a final list of venues on Friday with the International Rugby Board (IRB) but have secured an extension, understood to be for around a month.
West Ham are preferred tenants to take over the Olympic Stadium but a final deal between the Premier League football club and the London Legacy Development Corporation has still to be agreed.
That uncertainty has prevented tournament organisers from making a decision but they are keen to include the stadium if possible - especially as taking the sport into the heart of London's east end would show they were not merely going to traditional rugby areas.
After Friday's meeting with the IRB, a RWC statement said: "Both parties agreed that appropriate time should be given to allow every possible opportunity to include the Olympic Stadium, one of the world's most recognisable venues.
"The additional time will enable England Rugby 2015 to finalise negotiations and scheduling with other venues."
England Rugby 2015 chief executive Debbie Jevans said: "We are determined to select the best venues and deliver the optimum schedule for the Rugby World Cup, and are delighted to have received such strong support from the RWC Limited board for our proposals today.
"Our plans are on track and we are confident that we will finalise the schedule and the venues in the next few weeks."
RWC chairman Bernard Lapasset said that England 2015 was on track to be "an exceptional event" and that it was "the right thing for the tournament" to give organisers more time to explore the possibility of including the Olympic Stadium.
- Sports & Recreation
- International Rugby Board
- England Rugby