The travelling Europeans head to Chicago as holders of the trophy following a 14.5 points to 13.5 victory over the Americans at Celtic Manor in 2010.
However, this time around world number one McIlroy believes that the USA have a better 12-man squad.
"I think the United States are favourites, they are a strong team. We're going to have to play very well, we know that," McIlroy told reporters.
This will be McIlroy's second appearance at a Ryder Cup.