Sam Darnold suffered a hip injury in the first quarter of the Week 1 kickoff game against the Patriots and was ruled out for the remainder of the game after only one drive, replaced by Drew Lock (from the Drew Lock page).
That said, the wiki doesn't have specific details on the severity — no MRI results, timeline for return, or designation beyond "hip injury" and "ruled out." His status for Week 2 and beyond hasn't been updated yet. For now, consider him week-to-week at minimum, and Drew Lock is worth a waiver pickup in deeper formats if you need a QB fill-in.