Per the beat reporters on Twitter, Matt Harrison suffered a setback in his recovery from back surgery last month that necessitated him undergoing additional surgery this morning.
Despite the setback, again per these reports, Jon Daniels is saying that the timeline for his return hasn't necessarily changed, but the assumption is that he will be out for about three months, which would mean he'd be looking at returning around August 1.
Harrison, the Rangers' Opening Day starter this year, was looking to build on a pair of strong seasons in 2011-12, and establish himself as a legitimate #2 starter. However, Harrison struggled in his first two starts, and is going to likely miss at least half of this season.