SANTA CLARA – After two seasons in which the 49ers have been ravaged by injuries, the club is missing 18 players during the offseason program due to injuries.
"Just going off experience, this is the most time I've had with people missing OTAs," 49ers coach Kyle Shanahan said. "But we've been really healthy the last two OTAs, and it's been the opposite in (training) camp.
"So maybe it'll be the opposite this year. We're not healthy in OTAs, which might be a good sign for training camp."
First-round draft pick Nick Bosa was added to the list on Tuesday with a right hamstring injury. The severity of his injury is not known, but many other players are certain to sit out the remainder of the offseason program, which wraps up June 13.
Quarterback Jimmy Garoppolo took 20 snaps Tuesday in 7-on-7 drills and completed 75 percent of his pass attempts. But he will be held out of all 11-on-11 drills during the offseason program as a precaution after sustaining a torn ACL in his left knee in Week 4.
"It'll take him a while before he's able to protect himself and react, and keep people away from his legs," Shanahan said of Garoppolo.
Running backs Jerick McKinnon, Matt Breida and Raheem Mostert will not be available until training camp. McKinnon is returning from a torn ACL that wiped out his entire 2018 season. He is expected to be ready for the opening of training camp. Breida recently sustained a partially torn pectoral muscle in the weight room.
Breida did not require surgery, Shanahan said.
"It's frustrating for Breida because he can do just about everything," Shanahan said. "He just has to avoid contact. He can't be out there running with other people on the field."
Mostert sustained a fractured forearm in Week 9 against the Raiders and had surgery to insert a plate.
"They had to re-do the exact same thing," Shanahan said. "When it's not growing back together the right way it's better to just start it over. . . (It's) not too big of a deal, it just added another month."
Veteran tight end Garrett Celek, who sustained a concussion in Week 16 and was inactive for the season finale, has yet to be cleared from concussion protocol, Shanahan said. He is also experiencing problems with his back, which places his future in question.
"He can't get cleared from that until training camp, so (we're) going to have to be patient with him, too," Shanahan said.
Linebacker Fred Warner recently underwent arthroscopic surgery to clean out his knee and will not participate in OTAs, Shanahan said. The club expects him to be cleared for the start of training camp.
Linebacker Kwon Alexander (knee), cornerback Jason Verrett (Achilles), center Weston Richburg (knee-quadriceps) and rookie receiver Jalen Hurd (knee) are among the players who are not practicing due to surgeries from injuries sustained last season.