Triple-A Columbus placed Valera (hamstring) on its 7-day injured list Friday.
The outfield prospect suffered a strained hamstring early in spring training and is still working his way back from the injury, so he'll be inactive for the early part of the minor-league season. Valera, 23, slashed .211/.343/.375 with 10 home runs and one stolen base in 312 plate appearances for Columbus a season ago.