Greenlaw's appeal of a one-game suspension was denied by the NFL on Tuesday, Adam Schefter of ESPN reports.
The suspension stemmed from Greenlaw's actions during the 49ers' Week 5 win over the Seahawks, when he used his helmet to headbutt Ernest Jones during a skirmish on Seattle's sidelines. Greenlaw was unsuccessful in his appeal, so he'll be sidelined for San Francisco's Week 6 home game against the Commanders on Monday. With Garret Wallow (hamstring) facing a multi-game absence, Luke Gifford figures to step into a starting role at linebacker alongside Fred Warner and Jaden Dugger while Greenlaw is sidelined.