Lynch told reporters Thursday that Bosa doesn't have a "full-blown" high ankle sprain, but there are "components" of that injury. The defensive lineman will miss the remainder of the preseason due to the injury.
"We won't see him in the preseason and we'll go from there," Lynch said. "We'll get him right and he'll be a great player for a long time in this league. ... We don't feel he is injury prone. [Wednesday], he had a big human being fall on his leg while he was engaged with someone else.
"It's a significant ankle sprain, and there's that dreaded high ankle sprain. He doesn't have a full-blown one, but it has some components of that. ... It's safe to say we won't see him in the preseason and then we're going to be very prudent."
"Basically it's a minor high ankle sprain, but there's no such thing as a minor high ankle sprain because we know those are a much bigger deal than low ones," Shanahan said. "But we're hoping for Week 1."
The 49ers selected Bosa with the No. 2 overall pick in the 2019 NFL Draft out of Ohio State. He missed most of last season with the Buckeyes due to a core muscle injury.
Bosa also sat out most of the 49ers' off-season program because of a hamstring ailment.