"Just that Ahkello wasn't able to get a full week of practice in," Shanahan said this week. "We weren't going to throw Ahkello out there without covering a receiver at full speed in about seven weeks unless he could get three full days of practice in.
"We walked through about 80-percent of our reps that week. We walked through on Wednesday, and Friday and Thursday, we had two full-speed practices. Without getting the right amount of practice time in, it really wasn't much of a decision."
Moseley played 65 snaps against the Cardinals, but, once healthy, Witherspoon is expected to slide back into the starting role he had before suffering a foot sprain during Week 3. That could come as soon as Sunday night against the Green Bay Packers at Levi's Stadium, as the 49ers kick off a historically difficult three-game stretch.
There was some debate on who should start opposite Richard Sherman because Moseley has played well in Witherspoon's absence, who himself was playing at a high level before his injury.
Moseley, an undrafted second-year player, has allowed 19 receptions for 248 yards with a touchdown, an interception, and a passer rating of 81.3 on 32 targets this season, according to Pro Football Focus.
By comparison, Witherspoon allowed six receptions for 148 yards with a touchdown, an interception, and a passer rating of 59.5 on 18 targets before his injury, and was targeted once in his limited snaps on Sunday.