The 49ers believe Pettis (knee) avoided a long-term injury, but he's nonetheless scheduled for an MRI on Monday, Matt Maiocco of NBC Sports Bay Area reports.
Pettis was unable to return to Sunday's 29-27 loss to the Chargers after injuring his left knee on a punt return in the first quarter. He was replaced by Trent Taylor on special teams, with Kendrick Bourne stepping up to post a 3-34-1 receiving line as the No. 4 wide receiver. The initial optimism suggests Pettis avoided a major ligament injury, but the 49ers won't know for sure until they see results from the MRI.