With lower back inflammation, per Anthony Andro. This effectively solves the problem of whether to send down Taylor Teagarden or designate Omar Quantanilla for assignment, but is itself problematic in that Blanco is now racking up significant DL mileage with back injuries.
Quantanilla would have needed to clear waivers and accept an outright assignment back to Round Rock in order to keep him with the organization had he been designated for assignment, and there had been a bit of media speculation out there about him being a candidate to be plucked off waivers by some other ballclub. With this setback, one figures that Quintanilla will be here through at least September 1st, by which point the rosters will expand and his services can be retained on the active roster even after Blanco returns.
Darren O'Day will almost certainly be optioned back to Round Rock tomorrow to make room for Craig Gentry following his return from the seven-day disabled list; optioning Teagarden would leave the Rangers with just three bench players and an eight-man bullpen, which, for the lack of a better description, would make absolutely no sense.
Update: Per Evan Grant, Blanco's injury is "not an aggravation of the previous injury." He'll get a shot of anti-inflammatories today or Wednesday.