NFL insiders Ian Rapoport and Adam Schefter broke the news, adding that it remains unclear whether Bosa will be placed on injured reserve.
Bosa missed practice Thursday after previously sitting out Wednesday's session as a scheduled rest day. Schefter added that Bosa pulled his calf during Thursday's practice.
This is another setback for a 49ers defensive front that has already dealt with several injuries. The team is awaiting the return of Mykel Williams, who began the season on the physically unable to perform (PUP) list. He is expected to return to practice next week.
Defensive tackle Alfred Collins is out for the season after suffering a torn patellar tendon ahead of Week 1. Defensive end Sam Okuayinonu suffered a broken foot ahead of the season opener. Defensive tackles James Thompson Jr. (high-ankle sprain) and C.J. West (chipped bone in his knee) are expected to miss multiple weeks.
Rookie defensive end Romello Height underwent hand surgery this week, and his status for Sunday's game remains unclear.
Bosa has recorded seven tackles, two tackles for loss, and a quarterback hit through two games this season. While the pass rusher remains without a sack, defensive coordinator Raheem Morris spoke Thursday about Bosa's impact.
"He's been, really, the most dominant player without a sack," Morris said. "I have to say he's been awesome ... We'll see moving forward, all the stuff that happens with him, but he's been playing great."
The 49ers ranked last in the NFL with 20 sacks last season, making Bosa's health particularly important to San Francisco's pass rush. The defensive end returned from an ACL injury that forced him to miss all but the first three games of last season.
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