Upshaw who played for the Grand Rapid Drive, affiliate team of the NBA team Detroit Pistons, collapsed with 40 seconds left in their game against the Long Island Nets.
His family released a statement saying after continued efforts from the medical team looking after Upshaw, he was unable to gain consciousness.
He had reportedly suffered a cardiac arrest.
The 26-year-old went un-drafted in the NBA in 2014 before going on to play in Slovenia, until he was drafted in the G-League.
NBA G-League president Malcolm Turner said Upshaw was an outstanding young man who had an uncommon perseverance to be successful.
He also said he was a beloved member of the Drive and his continuous improvement and work ethic were hallmarks of his career.