McDonald was arrested last weekend on felony domestic violence charges, just days after NFL commissioner Roger Goodell announced a stricter discipline policy for domestic violence.
As of Wednesday, charges against McDonald had not yet been presented to the San Jose district attorney and the case was still under investigation. Harbaugh said Wednesday that McDonald was likely to play in Week 1 in respect of his due process, and Goodell said Thursday the NFL will let the legal process play out before ruling on any punishment for McDonald.
Under terms of the new policy, domestic violence offenders can be suspended six times for a first offense and can be banned from the NFL for life for a second offense. The new policy came in reaction to backlash against the NFL's decision to suspend Baltimore Ravens running back Ray Rice just two games for his domestic violence incident involving his then-fiancee.
McDonald, San Francisco's third-round draft pick in 2007, has made 16.5 sacks and 171 tackles in seven seasons with the team. The 49ers open the season on the road against the Dallas Cowboys.
- Ben Estes