Williams won the US Open in 2000 and 2001 and is now the second-oldest player to compete in the tournament in New York, after Renee Richards, who was 47 when she took part in 1981.
The US Open has another wildcard to hand out, and the AP news agency speculates that the organisers are waiting for a decision on whether sister Serena Williams also wants to play.
The siblings played doubles together in Cincinnati the other day, but were eliminated in the first round.
The US Open begins on August 30.
