Thomas underwent successful surgery to repair a rupture of the radial collateral ligament of his left thumb, according to the team. The injury, which could force the two-time All-Star to miss the start of the regular season, occurred during routine workouts on Monday.
"This was an unfortunate setback for Isaiah, but with his resolve and the top care he will receive from our medical team, we expect him to make a full recovery," Wizards general manager Tommy Sheppard said in a statement. "In the meantime, he will continue to mentor our young guards and have a positive impact on the team as we start training camp."
The procedure was performed Wednesday morning by Dr. Curtis Henn with assistance by Wizards orthopedist Dr. Wiemi Douoguih, according to the team. Washington opens the regular season Oct. 23 against the Dallas Mavericks.
Thomas signed a one-year contract with the Wizards on July 6 after spending last season with the Denver Nuggets.
Since entering the league as a second-round pick in the 2011 NBA Draft by the Sacramento Kings, he has averaged 18.6 points and 5.1 assists per game with the Boston Celtics, Phoenix Suns, Cleveland Cavaliers, Los Angeles Lakers, Nuggets and Kings.