Marsh was hurt after getting tangled in a pile during Wednesday's practice, the final one before Seattle broke training camp. The Seahawks have a light practice Thursday before Friday night's second preseason game against San Diego.
The team did not have any further details. Coach Pete Carroll is expected to talk after Thursday's practice.
Marsh was a fourth-round pick out of UCLA and was expected to contribute right away as a pass rusher for the Seahawks. Marsh had four tackles and a sack in Seattle's preseason opening loss to Denver.