Pettis worked on the side of the field to begin Monday's practice due to an undisclosed injury, Eric Branch of the San Francisco Chronicle reports.
It remains to be seen what sort of injury Pettis is dealing with, but any time missed due to injury could impact his Week 1 role. Coach Kyle Shanahan reiterated Sunday that Pettis is competing for a starting role, according to Matt Barrow of The Athletic, citing a lack of consistency for the second-year wideout. With Trent Taylor (foot) expected to miss the start of the regular season and Jalen Hurd (back) nursing an injury, San Francisco's wideout corps could struggle to provide depth until Pettis gets fully healthy regardless of whether he earns a starting gig.