"The prognosis is we're hoping he'll be ready to go within a week or two, but right now he has been pulled from the Futures Game," assistant general manager Thad Levine said.
The Rangers could be without a representative in the Futures Game. Catcher Jorge Alfaro, the organization's sixth-best prospect, has already been pulled from the game with a broken hand.
"We look at the Futures Game as a tremendous game for high-level prospects to showcase their talents," Levine said. "We're disappointed our prospects won't get the opportunity, but it doesn't diminish their value. We wish they had the opportunity to showcase their talents, but we need to get our guys healthy."
Class A Hickory second baseman Ryan Rua would be a good candidate to replace Gallo. He has 28 home runs, the most of any player in the Minor Leagues.
T.R. Sullivan is a reporter for MLB.com. Read his blog, Postcards from Elysian Fields, and follow him on Twitter @Sullivan_Ranger. This story was not subject to the approval of Major League Baseball or its clubs.