Sam Darnold is expected to miss roughly 4 weeks with the soft-tissue glute injury he suffered in Week 1, though he could return sooner — the Seahawks ruled him out for Week 2 but have no plans to place him on IR, which is usually a sign they expect him back mid-season (from the Sam Darnold page).
On Mayo Media Network, they noted the Seahawks have a favorable upcoming schedule with matchups against the Giants and Commanders, so they may not rush him back (). Drew Lock is filling in as the starter in the meantime.