Johnson, who has been struggling, to hit, was taking extra batting practice Friday and as a result has a stiff back that caused him to miss yesterday’s game. It is a minor injury and initially they thought he could play today, but by the end of the day yesterday Girardi said that it hadn’t improve as quick as they hoped it would and decided he’s going to get an extra day of rest. Like I said above, he’s expected to be back in the lineup Tuesday.
Bleacher Report - New York Yankees