A team spokesman said Wednesday that Williams suffered the injury while recently working out in Utah. He is expected to be ready to start training camp, which begins at Duke University Oct. 1.
Williams played through minor injuries all of last season and sat out a week in February with an ankle injury.
Williams, 29, is entering the second year of the five-year, $98 million contract he signed with the team in July 2012. He averaged 18.1 points, 7.7 assists and three rebounds a contest in 78 games last season.