FILE - United States' Michael Phelps and Singapore's Joseph Schooling check their times after a men's 100-meter butterfly heat during the swimming competitions at the 2016 Summer Olympics, Thursday, Aug. 11, 2016, in Rio de Janeiro, Brazil. Olympic gold medal swimmer Joseph Schooling has apologized for using cannabis in Vietnam while competing there on leave from military service in his native Singapore. Schooling achieved superstar status in Singapore when he won his country’s first and only Olympic title at the 2016 Rio de Janeiro Games. He won the 100 meters butterfly beating Michael Phelps in the American great’s last Olympic race. (AP Photo/Martin Meissner, File)

FILE - Singapore's Joseph Schooling looks at the scoreboard after a semifinal of the men's 100-meter butterfly during the swimming competitions at the 2016 Summer Olympics, Thursday, Aug. 11, 2016, in Rio de Janeiro, Brazil. Olympic gold medal swimmer Joseph Schooling has apologized for using cannabis in Vietnam while competing there on leave from military service in his native Singapore. Schooling achieved superstar status in Singapore when he won his country’s first and only Olympic title at the 2016 Rio de Janeiro Games. He won the 100 meters butterfly beating Michael Phelps in the American great’s last Olympic race. (AP Photo/Matt Slocum, File)

FILE - Singaporean swimmer Joseph Schooling attends a parliamentary meeting at the Parliament House in Singapore Monday, Aug. 15, 2016. Olympic gold medal swimmer Joseph Schooling has apologized for using cannabis in Vietnam while competing there on leave from military service in his native Singapore. Schooling achieved superstar status in Singapore when he won his country’s first and only Olympic title at the 2016 Rio de Janeiro Games. He won the 100 meters butterfly beating Michael Phelps in the American great’s last Olympic race. (AP Photo/Yong Teck Lim, File)