Jimmy Garoppolo spent the first 3 ½ seasons watching the measures a quarterback must take to protect himself.

Tom Brady is not the most nimble quarterback in the league, but nobody is better at buying time in the pocket with a step here or a step there to create enough space to deliver the ball down the field.

Most of the time, the ball comes out of Brady’s hand quickly -- before the pass rush arrives.

For the past three games while standing on the 49ers sideline, Garoppolo saw the beating a quarterback can take when pass protection does not hold up.

Coach Kyle Shanahan said he will make a decision on the 49ers’ starting quarterback before the team takes the practice field on Wednesday. Teams generally begin their preparations for upcoming opponents on Wednesdays.

Whomever starts at quarterback – rookie C.J. Beathard or Garoppolo, the newcomer – needs the full week of practice reps with the first-team offense to have his best chance of success on Sunday against the Chicago Bears, Shanahan said.

First off, it’s not even clear Beathard will be available to take part in a full week of practice. He sustained injuries to his left knee and hip on Sunday upon being taken down by Seattle defensive end Michael Bennett with a low hit after Bennett had already jumped offside.