Oswald has the job of monitoring the progress of London 2012
The International Olympic Committee has told London 2012 organisers they need to finalise venues for badminton and rhythmic gymnastics at the Games.
The sports were initially set to be held in a temporary arena, but could now be housed in existing facilities.
"I have to express a concern that three years before the Games their venue has not been finalised," chief co-ordinator for the Games Denis Oswald said.
However, London's chief executive Paul Deighton has moved to allay his fears.
"We are finalising our venue masterplan working with the two sports and we will have this resolved by the end of the year," he said.
"We are focusing right now on finding the right venue for the two sports that meets the needs of the athletes, legacy and costs and it has always been about balancing those," he said.
Both badminton and rhythmic gymnastics were originally planned to be located in a temporary venue called North Greenwich Arena 2. However, organisers are now looking to site them in existing venues, which could save £40m.
Speaking at an IOC meeting in Copenhagen, Oswald added: "London has still not yet achieved the final masterplan and two venues are still under discussion."
Oswald added that he was impressed by London's overall preparations, but stated the venues issue should be resolved before the next IOC visit in November.
Chairman of London 2012 Sebastian Coe told the session that the venues and Olympic Park would be ready "in plenty of time to test and practise".