Coach Kyle Shanahan ruled Pettis (knee) out for the 49ers' Week 5 contest against the Cardinals, Joe Fann of the team's official site reports.
Pettis departed Sunday's defeat to the Chargers in the first half and didn't return. After undergoing an MRI on Monday, he isn't a candidate to play Week 5, per Shanahan, indicating a significant knee injury. It remains to be seen if Pettis will miss time beyond this weekend, but Kendrick Bourne seemingly will benefit with fellow wide receiver Marquise Goodwin (thigh, hamstring) also tending to injuries.