U.S. stock index futures were marginally lower on Tuesday as investors awaited commentary from Federal Reserve officials through the day to gauge the central bank's policy stance after the latest downgrade of the United States' credit rating.

Traders currently expect at least two 25-basis-point rate cuts from the U.S. Federal Reserve by the end of the year, with the first expected in September, according to data compiled by LSEG. Fed officials on Monday flagged the ramifications of the latest downgrade of the U.S. government's sovereign credit rating and uneasy market conditions.

U.S. stock futures point to a lower open, a day after stocks made a comeback to close higher despite Moody's stripping the U.S. of its top AAA rating.