According to ESPN's Adam Schefter, the NFL will be releasing the preseason schedules for all 32 teams this afternoon. Regular season schedules will be released later this month.
Last season, the San Francisco 49ers faced the Minnesota Vikings, Houston Texans, Denver Broncos and San Diego Chargers in preseason. The San Diego Chargers appear regularly within the 49ers' preseason schedule and are usually the final opponent before the regular season.
One team that will once again not be on the 49ers preseason schedule are the Oakland Raiders. The 49ers and Raiders agreed not to play each other in preseason anymore after violence broke out at an August 20, 2011 matchup.