To clear a spot for him on the 25-man roster, the D-backs optioned reliever Esmerling Vasquez to Reno. The right-hander had appeared in three games and allowed three runs in three innings.
In order to add Benson to the 40-man roster, the D-backs transferred pitcher Brandon Webb from the 15-day to the 60-day disabled list.
Players who are on the 60-day disabled list do not count against a team's 40-man roster.
Webb, who has not pitched since Opening Day of last season, has been playing catch but is not close to returning to game action. He is eligible to come off the disabled list on May 25.