Putin plans to "shake his hand" along with other leaders' when he greets them at the summit in Saint Petersburg, Ushakov said.
The two will still have a chance to speak on the sidelines of the summit, Ushakov said. "Whether it will be standing up or in chairs, I do not know," he commented.
With US-Russia ties at a new low after Moscow gave asylum to US intelligence leaker Edward Snowden, the White House earlier this month scrapped a US-Russia summit that was planned to take place in Moscow just ahead of the G20.
A bilateral meeting in Saint-Petersburg was not scheduled "because we and the Americans planned a full-scale state visit (by Obama) to the country, which, as you know, is not happening," Ushakov explained.
As well as the row over Snowden, US-Russia ties have been stretched by a host of other rows, ranging from Syria to human rights.