According to The Athletic's Andrew Baggarly, manager Bruce Bochy told reporters Wednesday that Belt's season is "likely over." Belt has missed the Giants' last four games because of soreness in his right knee.
Belt previously landed on the disabled list in late July after he suffered a hyperextended knee. That injury cost him 17 games.
Since returning to the diamond Aug. 14, Belt hasn't set the world on fire. He batted .185 in August, and he followed up with a .125 average in September before hitting the shelf again.
If his season is over, Belt will finished the year with a .253/.342/.414 slash line, 14 home runs and 46 RBI across 456 plate appearances.
Aramis Garcia, who is hitting .346 since getting called up Aug. 26, should serve as San Francisco's primary option at first base with Belt sidelined.