Per The Athletic's Shams Charania and Joe Vardon, Williamson was being attended to by members of the Pelicans medical staff but is said to be "fine" and the cramping is "not an issue."
The Pelicans announced on Thursday morning that Williamson had left the NBA campus in Florida to tend to "an urgent family medical matter" and that he will return "at a later date."
Charania and Vardon noted that Williamson's cramping issue wasn't the reason that he left.
Per ESPN's Tim Bontemps, who obtained a copy of the NBA's health-and-safety protocol manual issued to all players and staffers, anyone who leaves the campus with prior approval from the league will be subject to a four-day quarantine upon returning pending one of two things:
"He is gone fewer than seven days, and during each day off campus, he is tested for COVID-19, and the result(s) are negative.
"He leaves for an extended absence and undergoes a daily COVID-19 test that comes back negative for at least the seven days before he arrives back on campus."
The Pelicans didn't specify when Williamson might return as they continue to prepare for the season to restart.
Williamson's rookie season got off to a delayed start because of a torn meniscus that required surgery in October. The 20-year-old made his debut on Jan. 22, scoring 22 points in 18 minutes against the San Antonio Spurs. He averaged 23.6 points, 6.8 rebounds and 2.2 assists in 19 games before the season was suspended on March 11.
The Pelicans are scheduled to play the Utah Jazz on July 30 at 6:30 p.m. ET in the first game of the resumed season.