Shams Charania of Yahoo Sports added the ailment could cost Thompson "several games", but he's expected back by month's end. He will be re-evaluated on March 22.
The injury - originally believed to be a simple sprain - will keep Thompson out for at least four more games.
In either case, Thompson is sidelined by an injury sustained in the fourth quarter of a loss to the Timberwolves on Sunday in Minnesota.
Teachers not backing down: Rally against pension bill brings hundreds to Frankfort
However, some state officials have pointed out that it could save taxpayers $3.2 billion over the next two decades. The raises would go back to 1.5 percent once the system is at least 90 percent funded, under the proposal.
Thompson, 28, is averaging 19.7 points and shooting at a 44 percent clip from distance on the season.
Injuries to these three All-Stars are not considered to be serious, sources said.
This is a clear sign the defending champions are valuing health heading into the playoffs, rather than making a run at the No. 1 seed.
Golden State is now 8-2 in their last 10 games, but trailing the Houston Rockets by two full games in the race for first place in the West.