Richardson, the Warriors' leading scorer last season with 23.2 points per game, was hurt during the second quarter. After X-rays at Arco Arena revealed the break, Richardson was placed in a cast by the Kings' medical staff.
Richardson, who had five points when he was injured, is averaging just 13.1 points and 4.1 rebounds this season. He missed eight games earlier in December with a bone bruise in his left knee.
The sixth-year pro increased his scoring average in each of the last four seasons but has struggled since undergoing arthroscopic surgery on his left knee in August. Richardson has shot poorly all season, making just 37.7 percent of his shots -- worst among the Warriors' regulars.