Greene, 29, has played parts of four seasons with the Cardinals and part of last year with the Astros, who he was in camp with this past Spring Training. The right-handed hitter and top pick by the Cardinals in the 2005 First-Year Player Draft has played big league games at every position except pitcher and catcher.
He was hitting .265 with four RBIs in eight games for the Knights after agreeing to terms with the White Sox on a Minor League contract on April 4.
"It's been an experience the last couple weeks, going through that at the end of Spring Training," said Greene, who was released by the Astros at the end of March. "It was the first time I experienced something like that. Kind of a new thing. I was fortunate, thankful to get hooked up with the White Sox and really excited to be up here.
"After I cleared waivers, they were in talks with my agent about getting me over with them. It definitely was a good route."
With Conor Gillaspie set at third and Jeff Keppinger at second in the absence of Gordon Beckham, Greene moves into Sanchez's vacated utility role. Basically, Greene has been told to be ready for anything.
"We know he's a good player," said White Sox manager Robin Ventura of Greene, who found out Saturday about his promotion and owns a .224 career average with 16 homers, 58 RBIs and 28 stolen bases in 266 games. "He can play infield, a little bit of outfield in an emergency. We'll find out."
Scott Merkin is a reporter for MLB.com. Read his blog, Merk's Works, and follow him on Twitter @scottmerkin. This story was not subject to the approval of Major League Baseball or its clubs.