Scottsdale Police Officer Dave Pubins said in an email to the Arizona Republic Beasley's actions are being scrutinized following a complaint by an unidentified woman.
"At this point we are investigating an allegation into a sex assault charge made against Michael Beasley," Pubins wrote. "There is no booking photo as he was not arrested or charged with a crime. This investigation is ongoing."
A police report indicated the woman made the complaint in connection with an alleged incident at Beasley's home in January, the newspaper said.
The 23-year-old former No. 2 overall draft pick of the Minnesota Timberwolves averaged 10.1 points and 3.8 rebounds over 75 games last season for Phoenix.
He was cited for driving with a suspended license earlier this year.