According to the Wizards, Thomas ruptured the radial collateral ligament in his thumb during a routine workout 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,” Washington 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 injury is the latest setback for Thomas, who has only appeared in 44 games over the past two seasons.
Since setting career-highs with 30.8 points and a .463 field goal percentage in 2016-17 with the Boston Celtics, Thomas has been dealing with an ongoing hip injury. He underwent surgery on his hip near the end of the 2017-18 season and was limited to only 12 games with the Denver Nuggets last year while recovering.
Thomas was signed as a free agent by the Wizards on July 6. Shortly after, he told reporters at the Las Vegas Summer League that he was feeling healthy and was ready to return to the court.
“I’m feeling great. I’m back to feeling like my old self,” Thomas told The Washington Post. “I’ve been healthy for a while. This is the first summer in two years where I can really work on my body and work on my game. If you let that sink in, that sounds crazy.”