Rookie Trey Lance will make his first NFL start Sunday for the 49ers after a shaking outing replacing Jimmy Garoppolo in Week 4. Sources said Garoppolo's calf injury has roughly a 70% chance of healing enough to allow him to take over the reins in Week 7, but Lance could certainly render that less significant if he shines today.

Garoppolo has long understood that Lance was, in all likelihood, going to get the chance to play more as the season went along, and it was never lost on him that a transition was forthcoming, sources said. The calf injury he suffered was "significant" and all but certain to keep him out for this week, though head coach Kyle Shanahan did not rule him out until late in the week.

Lance getting a full workweek, and the 49ers struggling to run the ball as they are accustomed to doing, could bode well for the North Dakota State product. Lance barely played last year in college and has been sharing reps to this point, so a heavier practice workload is essential. Lance looked frazzled early last week when Garoppolo's injury forced him into extended duty, but at this point Shanahan's whole focus is on designing a game plan for the rookie that can help the 49ers beat an undefeated Arizona team.

San Francisco's offense has been erratic thus far, with injuries to its running backs playing a key role. Its outside zone rushing scheme has not been nearly as impactful as usual, though Lance's unique athleticism and multiplicity in the option game could help unlock the ground attack. He played very sporadically in the first few weeks, but he'll know going into Sunday that he doesn't have to try and make every play a splash play with a full game ahead.

There is no doubt right now that Garoppolo is the more polished and more ready quarterback to execute the offense, but if Lance is able to make an impact running the ball and settles down with his decision making and accuracy, his role could quickly expand moving forward.