Both sustained knee injuries during last week's game, and the team ruled them out as expected Saturday.
Forte has mostly been a model of durability in his eight seasons. But now that he is unavailable, a bigger load falls to rookie Jeremy Langford. Royal was with Chargers last three seasons.
Center Hroniss Grasu is doubtful because of a neck injury.
The Bears (2-5) are coming of a 23-20 loss to Minnesota. The Chargers (2-6) were beaten by Baltimore 29-26 last week.