The 23-year-old Watanabe is a native of Japan who moved to the United States in 2013 and played collegiately at George Washington. After going undrafted last month, the 6-foot-9 Watanabe averaged 9.4 points, 4.2 rebounds and 1.6 blocks in five games for the Brooklyn Nets' summer league team in Las Vegas.
Henry, who is 6-foot-6, played in 20 games for the Grizzlies this past season after signing a two-way contract Jan. 13.
The 25-year-old Henry averaged 5.4 points, 1.9 rebounds, 1.1 assists, 1.6 steals and 18.9 minutes for the Grizzlies. He also averaged 16.4 points, 5.2 rebounds and 2.1 assists in the NBA G League for the Oklahoma City Blue and Memphis Hustle.