The former New England Patriots backup was traded to San Francisco on Halloween in exchange for a second round pick in the 2018 NFL Draft.
He stepped in for his first action of the 2017 season on Sunday, late in the 49ers' 24-13 loss to the Seattle Seahawks. Garoppolo came into the game after 49ers starter C.J. Beathard was injured with about a minute remaining in the NFC West clash at Levi's Stadium.
Garoppolo completed 2-of-2 pass attempts for 18 yards and a touchdown. He left the loss with a 143.7 quarterback rating. He began his debut by taking a shotgun snap for a four-yard run to the Seahawks' 14-yard-line. His next play was an eight-yard pass to Aldrick Robinson to the right side for a first down.
But the play of the day for Garoppolo came with just two seconds left in the game. The quarterback took the 49ers no-huddle before rolling out and firing a 10-yard pass to Louis Murphy for a touchdown, the lone score of the day for his new squad.
Garoppolo stood in the pocket for a minute on that play before feeling the pass rush. He then jetted to his left, but continued to look for an open receiver. He eventually found one, before setting his feet at the 20-yard-line and stabilizing his body. He planted both feet in the ground for a second before firing the pass between Murphy and the sideline for a touchdown.
Beathard completed 22-of-38 passes for 201 yards and an interception in the loss.
Shanahan said Beathard would get an X-Ray on Monday, but he might have a bruise on his lower left leg from a hit received from a helmet or shoulder pad.
The first-year head coach also said that the three plays Garoppolo handled would not factor into if he would start for the 49ers.
"No, those plays have nothing to do with anything," Shanahan told reporters. "That's just running around and made a great play, but those have no bearing on it at all."
"I just said we're going to watch the tape, see how guys feel. We'll work with him Monday and Tuesday and then put a game plan together and see what we decide for Wednesday."
The 49ers face the Chicago Bears at 1 p.m. Sunday at Soldier Field in Chicago.
"There's never an easy situation to go into, being the backup," Garoppolo told reporters. "I've experienced both ends of it. You always have to be ready. I've been saying it for the past four years. You never know when your time is going to come, if it's going to come, so when it does you've got to take advantage of it."