Garoppolo's return to the starting lineup has not been in question since Friday, when coach Kyle Shanahan announced Garoppolo's right ankle has healed well enough for him to return to the starting lineup.
C.J. Beathard is the 49ers' No. 2 quarterback, as Nick Mullens was announced Sunday morning as one of the team's six inactive players for the team's Week 5 game against the Miami Dolphins at Levi's Stadium.
Mostert returns to action after sitting out the past 2 1/2 games with a knee sprain. Both Mostert and Garoppolo did not return to play in the second half of the 49ers' game against the New York Jets on Sept. 20.
Mostert went through limited practices on Wednesday, Thursday and Friday. When Mostert left the lineup, he was the team's leading rusher with 148 yards on 23 rushing attempts (6.4-yard average).
It is not certain whether Mostert or Jerick McKinnon will get the bulk of the action on Sunday. McKinnon started both games in Mostert's absence. McKinnon has 193 yards and three touchdowns rushing on 34 carries (5.7 average).
Wide receiver Deebo Samuel, who was not allowed into the 49ers' Santa Clara facility on Thursday and Friday due to a non-COVID-19 illness, was cleared on Saturday and will suit up against the Dolphins.
This season, any time a player experiences symptoms of an illness, he must self-isolate and pass two coronavirus tests before rejoining his teammates. Samuel had a fever and was achy early in the week, coach Kyle Shanahan said.
On Friday, Samuel was feeling fine and was asymptomatic, Shanahan said.
The 49ers announced Dante Pettis as one of their inactive players.
The 49ers were hoping for wide receiver Richie James to return after going on injured reserve following Week 1 due to a hamstring injury. The 49ers cut veteran receiver Mohamed Sanu during the week. On Saturday, the club elevated receiver Kevin White from the practice squad.
White was the No. 6 overall pick of the Chicago Bears in 2015. In 14 games in his injury-plagued career, White has just 25 receptions for 285 yards and no touchdowns. White is getting the call to suit up over Pettis, a second-round pick of the 49ers in 2018.