Harbaugh, speaking at his final press conference of the season, revealed Gore fractured his right ring finger during the 23-17 defeat.
The 49ers' all-time leading rusher will need minor surgery, CSN Bay Area reported.
Gore was limited to 14 yards on 11 carries with a 17-yard pass reception in the NFC title game.
"I did not know about it until after the game," Harbaugh said.
Gore finished the season with 1,128 rushing yards on 276 times carries, scoring nine touchdowns.