"Don't know the severity of it," head coach Kyle Shanahan said afterward, according to Matt Maiocco of NBC Sports Bay Area.
The injury occurred during one-on-one drills.
Bosa is no stranger to the injury bug, as he missed most of his junior season at Ohio State while recovering from a core muscle ailment and tore his ACL while in high school.
He and Dee Ford, both newcomers, are expected to vastly improve a San Francisco pass rush that struggled to generate pressure on opposing quarterbacks a year ago.
Running backs Matt Breida and Raheem Mostert missed practice completely, and neither is slated to participate in OTAs. Breida suffered a pectoral injury in the weight room, while Mostert encountered a setback in his recovery from a broken forearm. Both players are expected to be ready for training camp, Shanahan said, according to David Bonilla of 49ers Webzone.
In more positive news, quarterback Jimmy Garoppolo threw at practice as he continues to progress from the torn ACL that derailed his 2018 season.
Garoppolo isn't expected to be cleared for 11-on-11 drills until training camp.