The 49ers officially placed Garoppolo (ankle) on injured reserve Thursday, Nick Wagoner of ESPN.com reports.
The transaction was merely a formality, as head coach Kyle Shanahan admitted Wednesday that Garoppolo could be done for the season after aggravating a high-ankle sprain in last week's loss to the 49ers. At the very least, Garoppolo will have to miss three games by virtue of landing on IR, so the 49ers will turn the offense over to Nick Mullens in the meantime.