Ehrhoff left the game after a fight with Washington's Troy Brouwer late in the first period and did not return.
Buffalo coach Lindy Ruff said Ehrhoff was going to "miss some time ... probably weeks." Ruff did not disclose Ehrhoff's injury.
The Sabres traded for Ehrhoff this summer and signed him to a 10-year, $40 million contract. He has three goals and 14 assists this season.